Add circuit breaker configuration support

[currantw]

Summary

Add CircuitBreakerConfig to the client configuration, matching the existing implementation in Java, Python, Node, and Go (valkey-io/valkey-glide#6050). The circuit breaker logic lives in the Rust core — this task adds the config class, serializes it via FFI, and surfaces the CircuitBreakerException type to callers.

Issue Link

Closes #474.

Features and Behaviour Changes

• New CircuitBreakerConfig class with fluent WithXxx() API for configuring the client-wide circuit breaker
• New Errors.CircuitBreakerException thrown when the breaker is open and requests are rejected
• ConnectionConfiguration builder gains WithCircuitBreaker(CircuitBreakerConfig) method
• All config properties are optional — unset properties use Rust core defaults

Implementation

• CircuitBreakerConfig.cs: Sealed class with nullable properties, fluent setters with validation, and ToFfi() conversion
• Errors.cs: Added CircuitBreakerOpen = 4 to RequestErrorType enum and CircuitBreakerException class
• FFI.structs.cs: Added CircuitBreakerConfig readonly struct (primary constructor pattern) and wired through ConnectionRequest
• ConnectionConfiguration.cs: Added field to ConnectionConfig record and builder method
• rust/src/ffi.rs: Added CircuitBreakerConfig FFI struct and conversion in create_connection_request(). Also simplified existing code with then_some/then/transpose patterns.

Limitations

• Only standalone server positive test (trip + assert exception) — cluster positive test would require pausing individual cluster nodes
• Documentation page at https://glide.valkey.io/how-to/connections/circuit-breaker/ does not yet have C# examples (tracked in Add C# examples to circuit breaker documentation page valkey-glide-docs#273)

Testing

• 23 unit tests (CircuitBreakerConfigTests.cs): defaults, validation, fluent chaining, builder integration
• 9 integration tests (CircuitBreakerTests.cs):
  • Default/custom config connects successfully (standalone + cluster)
  • Does not interfere with normal operation (aggressive thresholds)
  • No false positives under load (200 sequential commands)
  • Positive test: trips on timeouts and rejects with CircuitBreakerException
• All tests pass locally

Related Issues

• Core, Java, Python, Node, Go: Add client-wide circuit breaker valkey-glide#6050 (upstream circuit breaker feature)
• Add client-wide circuit breaker valkey-glide#5996 (circuit breaker design)
• Add C# examples to circuit breaker documentation page valkey-glide-docs#273 (C# docs for circuit breaker page)

Checklist

• This Pull Request is related to one issue.
• Commit message has a detailed description of what changed and why.
• Tests are added or updated and all checks pass.
• CHANGELOG.md, README.md, DEVELOPER.md, and other documentation files are updated.
• Destination branch is correct - main or release
• Create merge commit if merging release branch into main, squash otherwise.

[Copilot]

Pull request overview

This PR adds circuit breaker configuration support to the Valkey GLIDE C# client by introducing a public CircuitBreakerConfig API, wiring the configuration through the C#↔Rust FFI boundary, and surfacing a dedicated CircuitBreakerException when the core rejects requests due to an open breaker.

Changes:

• Introduces CircuitBreakerConfig with fluent WithXxx() setters and FFI serialization.
• Wires circuit breaker config through ConnectionConfiguration and the FFI ConnectionRequest/Rust ConnectionConfig.
• Adds Errors.CircuitBreakerException plus unit/integration tests covering config and behavior.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/Valkey.Glide.UnitTests/CircuitBreakerConfigTests.cs	Adds unit tests for default/unset behavior and validation of the new config API.
tests/Valkey.Glide.IntegrationTests/CircuitBreakerTests.cs	Adds integration tests to validate circuit breaker config doesn’t break connectivity and trips/rejects when expected.
sources/Valkey.Glide/Internals/FFI.structs.cs	Extends the marshalled connection request to include circuit breaker config fields and struct layout.
sources/Valkey.Glide/Errors.cs	Adds CircuitBreakerException and maps a new RequestErrorType to it.
sources/Valkey.Glide/ConnectionConfiguration.cs	Adds builder/property plumbing to attach circuit breaker config to client connection configuration.
sources/Valkey.Glide/CircuitBreakerConfig.cs	New public config type with validation, fluent API, and ToFfi() conversion.
rust/src/ffi.rs	Adds FFI-side circuit breaker struct and converts it into the core client request.
CHANGELOG.md	Documents the new circuit breaker configuration feature in the changelog.

Comments suppressed due to low confidence (2)

sources/Valkey.Glide/CircuitBreakerConfig.cs:74

• WithFailureRateThreshold currently allows NaN/Infinity because the range checks do not catch those values. Passing NaN through FFI can cause undefined circuit breaker behavior in the core. Reject non-finite values explicitly before the range checks.

        ArgumentOutOfRangeException.ThrowIfLessThanOrEqual(threshold, 0.0, nameof(threshold));
        ArgumentOutOfRangeException.ThrowIfGreaterThan(threshold, 1.0, nameof(threshold));
        FailureRateThreshold = threshold;

sources/Valkey.Glide/CircuitBreakerConfig.cs:100

• ToFfi() casts OpenTimeout.TotalMilliseconds to uint. For very large timeouts (> ~49.7 days), this overflows and can silently wrap in an unchecked cast. Validate an upper bound when setting the value so the marshalled value stays accurate.

        ArgumentOutOfRangeException.ThrowIfLessThanOrEqual(openTimeout, TimeSpan.Zero, nameof(openTimeout));
        OpenTimeout = openTimeout;

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[jeremyprime]

As mentioned in comments on the PHP PR I think we should ensure consistency between all the clients, the key pieces being (A) having the CB defaults in the client, and (B) not worrying about config edge case validation (until valkey-io/valkey-glide#5937, although you already have it here so that's fine).

[currantw]

Made the following changes for consistency with other clients:

• Added default values in the client
• Remove unnecessary edge case validation
• Removed integration tests

However I didn't retain some edge case validation for these two cases:

• TimeSpan (window size and open timeout). The client validates that these can fit in u32 to avoid overflow.
• Zero values. Since the Rust core uses zero as a default value for many of these properties, I also validate that these values cannot be set to zero by the user. These aren't valid values, and if we allowed them, the user would get some unexpected results!