Support custom socket address resolution

[affonsov]

Summary

Ports the custom socket address resolution feature from valkey-glide to the C# client. Allows users to provide a callback that intercepts and rewrites server host/port pairs before the client establishes connections - useful for routing through proxies or custom DNS resolution.

Issue Link

This pull request is linked to issue: N/A (porting from upstream valkey-glide)

Features and Behaviour Changes

• New public delegate AddressResolverDelegate in ConnectionConfiguration:

  public delegate (string host, ushort port) AddressResolverDelegate(string host, ushort port);

• New WithAddressResolver() builder method on both StandaloneClientConfigurationBuilder and ClusterClientConfigurationBuilder
• Feature is fully opt-in - null by default, no behaviour change for existing clients
• If the resolver throws an exception or returns invalid values (empty host, port 0, oversized hostname), the client falls back to the original address and logs an error (consistent with Java client behavior)

Implementation

Follows the direct FFI callback pattern (same as Go PR valkey-io/valkey-glide#5891), not the socket listener/registry pattern used by Python and Node.

• Updated valkey-glide submodule to b4b34a1dc16d to include the core Rust AddressResolver trait (PR #5328) and the FFI layer changes (PR #5876)
• Added AddressResolverCallback C function pointer type and FFIAddressResolver struct to rust/src/lib.rs
• Updated create_client Rust FFI function with an optional 5th address_resolver parameter
• C# side marshals the managed delegate to a native function pointer and passes it to the Rust layer; the delegate is held as a field to prevent GC collection

Limitations

• The resolver is called once per address at connection time; it is not called on reconnection attempts (same behaviour as other language bindings)
• Maximum resolved hostname length is 1024 bytes

Testing

• Unit tests in ConnectionConfigurationTests.cs covering builder configuration, defaults, and edge cases
• Integration tests in AddressResolverTests.cs covering:
  • Identity resolver is invoked and client connects successfully (standalone and cluster)
  • Resolver that throws an exception falls back to original address
  • Resolver returning empty host falls back to original address
  • Resolver returning port zero falls back to original address
  • Resolver returning oversized hostname falls back to original address

Related Issues

• Support custom socket address resolution valkey-glide#5328 - Java: Support custom socket address resolution (core Rust infra)
• Python: Support custom socket address resolution valkey-glide#5876 - Python: Support custom socket address resolution (FFI layer)
• Node: Support custom socket address resolution when connecting to valkey valkey-glide#5890 - Node: Support custom socket address resolution
• Go: Support custom socket address resolution valkey-glide#5891 - Go: Support custom socket address resolution

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.