Replace IReadOnlyDictionary with IEnumerable<KeyValuePair>

[drasticactions]

Fixes #12

[Copilot]

Pull request overview

This PR fixes an AT Protocol query-parameter serialization bug where endpoints requiring repeated query keys (e.g. app.bsky.feed.getPosts?uris=a&uris=b) previously failed due to Dictionary.Add collisions. It updates the public client API and the URL-building/generation pipeline to use an IEnumerable<KeyValuePair<string,string>> parameter model that can represent repeated keys.

Changes:

• Replaces IReadOnlyDictionary<string, string> query-parameter plumbing with IEnumerable<KeyValuePair<string, string>> across IATProtoClient and HTTP URL building to support repeated query keys.
• Updates the source generator to emit a sequence of KeyValuePair entries (one per array item) instead of building a dictionary.
• Adds unit tests for repeated-key query serialization and for the generator output; updates the AuthTest sample to demonstrate multi-URI getPosts.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/CarpaNet.UnitTests/Identity/IdentityResolverTests.cs	Updates mock client interface signatures to match the new query-parameter type.
tests/CarpaNet.UnitTests/Http/XrpcHttpHandlerTests.cs	Adds coverage ensuring repeated keys serialize as repeated query parameters.
tests/CarpaNet.UnitTests/Generation/ApiGeneratorTests.cs	Adds tests asserting generated parameter classes emit KeyValuePair sequences and avoid dictionaries for arrays.
src/CarpaNet/IATProtoClient.cs	Changes public interface GET/Subscribe parameter type to IEnumerable<KeyValuePair<string,string>>.
src/CarpaNet/Http/XrpcHttpHandler.cs	Updates URL building APIs to accept IEnumerable<KeyValuePair<...>> and emit repeated query params; adjusts repo-resolution lookup logic.
src/CarpaNet/ATProtoClient.cs	Propagates the new parameter type through the concrete client implementation.
src/CarpaNet.SourceGen/Generation/ApiGenerator.cs	Changes generated ToDictionary() implementation to return a sequence of KeyValuePair entries (supporting repeated keys).
src/CarpaNet.OAuth/ATProtoOAuthClient.cs	Updates OAuth client implementation signatures to match the new parameter type.
samples/AuthTest/Program.cs	Adds an interactive “Get posts by URIs” sample flow exercising repeated uris query parameters.
samples/AuthTest/AuthTest.csproj	Resolves the app.bsky.feed.getPosts lexicon for the new sample usage.

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