feat(http): add standard hedging handler

[thomhurst]

Closes #127.

What changed

• add AddStandardHedgingShield and bindable StandardHedgingShieldOptions
• compose total timeout and hedging with endpoint-local concurrency limits, circuit breakers, and attempt timeouts
• preserve safe replay rules, ordered/weighted routing, state isolation, and exact response/request disposal
• document the one-line registration and add HTTP benchmarks

Validation

• dotnet build Kevlar.slnx -c Release --no-restore
• dotnet run --project tests/Kevlar.Tests -c Release --no-build -- --timeout 5m — 680 passed
• dotnet run --project tests/Kevlar.IntegrationTests -c Release --no-build -- --timeout 5m — 117 passed
• npm run build in docs/
• Verify-Packages.ps1 — layout, consumers, analyzers, trimmed and single-file publish passed; NativeAOT remains Linux-CI-only
• Verify-DocSnippets.ps1 — 99 snippets compiled and documented behavior executed

Benchmark

ShortRun, .NET 10, HTTP happy path:

Method	Mean	Allocated
Manual composition	1.964 us	3.41 KB
Standard registration	1.977 us (1.01x)	3.41 KB (1.00x)

[thomhurst]

Rebased onto #131 and resolved the standard-handler docs/guard overlap by preserving both APIs. The Windows failure reproduced locally as a real gRPC deadline race: TestServer can surface Unavailable after the deadline. Added deterministic coverage and normalized that expired transport status to DeadlineExceeded while preserving trailers. Release build, 685 unit tests, and 118 integration tests pass locally.

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📥 Commits

Reviewing files that changed from the base of the PR and between e6327f4 and 28e64c6.

📒 Files selected for processing (10)

• benchmarks/Kevlar.Benchmarks/HttpStandardHedgingBenchmarks.cs
• docs/docs/http.md
• src/Kevlar.Extensions.Grpc/ShieldUnaryClientInterceptor.cs
• src/Kevlar.Extensions.Http/PublicAPI.Unshipped.txt
• src/Kevlar.Extensions.Http/ShieldHttpClientBuilderExtensions.cs
• src/Kevlar.Extensions.Http/StandardHedgingShieldOptions.cs
• tests/Kevlar.IntegrationTests/GrpcResilienceTests.cs
• tests/Kevlar.IntegrationTests/HttpReplayTests.cs
• tests/Kevlar.IntegrationTests/HttpResilienceTests.cs
• tests/Kevlar.Tests/HttpContractTests.cs

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