Sync latest vendored TestFx protocol changes

[Evangelink]

Summary

• synchronize tracked TestFx files and vendored baselines to microsoft/testfx@dba319b212caae2a325800de8a5570ebe787b06d
• consume optional retry AttemptNumber handshake metadata so multiple test-host instances can share one attempt, while retaining instance-based inference for older hosts
• synchronize file-artifact Kind field ID, model, and serializer support
• make retry state updates thread-safe for concurrent test-host shards

Fixes #55255

Compatibility

Both protocol additions are optional and additive. Older peers continue to omit them, and unknown fields remain skippable.

Validation

• built src\Cli\dotnet\dotnet.csproj
• built test\dotnet.Tests\dotnet.Tests.csproj
• 43 focused dotnet.Tests passed
• vendored manifest validation and dry-run drift check report 30 entries, 38 sources, and 0 drift

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[Copilot]

Pull request overview

Synchronizes the dotnet test <-> Microsoft.Testing.Platform (TestFx) vendored protocol surface in dotnet/sdk to match upstream changes, including an optional retry attempt number handshake property, an added file-artifact Kind field, and thread-safe retry/progress state updates for concurrent/sharded hosts.

Changes:

• Consume optional AttemptNumber handshake metadata to correctly attribute multiple host instances (shards) to the same retry attempt, while preserving legacy instance-based inference when absent.
• Extend the file-artifact IPC model/field IDs/serializer to support the optional Kind field and log it.
• Make retry/progress state updates thread-safe (assembly run map + per-assembly progress state) and add focused regression tests.

Show a summary per file

File	Description
test/dotnet.Tests/CommandTests/Test/TestProgressStateTests.cs	Adds regression tests for explicit attempt-number semantics and concurrency across shards.
test/dotnet.Tests/CommandTests/Test/TestApplicationHandlerTests.cs	Adds a test ensuring an explicit attempt number is surfaced in terminal output; updates test handshake builder to optionally include it.
test/dotnet.Tests/CommandTests/Test/FileArtifactMessagesSerializerTests.cs	New test validating FileArtifactMessage.Kind round-trips through the serializer.
src/Cli/dotnet/Commands/Test/MTP/TestApplicationHandler.cs	Parses optional AttemptNumber from handshake and forwards it into terminal reporting; logs artifact kind.
src/Cli/dotnet/Commands/Test/MTP/Terminal/TestProgressState.cs	Introduces locking and attempt-number mapping to make retry/result accounting thread-safe and shard-aware.
src/Cli/dotnet/Commands/Test/MTP/Terminal/TerminalTestReporter.cs	Threads attempt number through AssemblyRunStarted, ensures safe assembly-run creation under concurrency, and uses per-instance attempt numbers for output.
src/Cli/dotnet/Commands/Test/MTP/Terminal/SimpleTerminalBase.cs	Minor comment update while syncing vendored content.
src/Cli/dotnet/Commands/Test/MTP/IPC/Serializers/FileArtifactMessagesSerializer.cs	Adds read/write support for optional Kind field and updates field counting.
src/Cli/dotnet/Commands/Test/MTP/IPC/ObjectFieldIds.cs	Adds the FileArtifactMessageFieldsId.Kind field id (wire contract alignment).
src/Cli/dotnet/Commands/Test/MTP/IPC/Models/FileArtifactMessages.cs	Extends FileArtifactMessage model with optional Kind.
src/Cli/dotnet/Commands/Test/CliConstants.cs	Adds optional handshake property id AttemptNumber (vendored constants alignment).
eng/vendored-files.json	Updates baseline SHAs to the referenced upstream microsoft/testfx commit.

Copilot's findings

• Files reviewed: 12/12 changed files
• Comments generated: 0