Fix flaky MCP adapter activity snapshot tests

[glen-84]

Summary

• McpAdapterActivityTests captured the ASP.NET Core HttpRequestIn server span for the MCP streamable-HTTP transport request, whose terminal status is nondeterministic relative to the capture window, making the activity snapshots flaky.
• MatchActivitySnapshot now strips top-level HttpRequestIn roots before snapshotting, mirroring FusionMcpAdapterActivityTests; both helpers carry reciprocal keep-in-sync comments.
• Regenerated the affected MCP snapshots across both target-framework variants.

Test plan

• McpAdapterActivityTests green on net10.0 and net11.0.
• Looped the class 50× on net11.0 with no failures.

[Copilot]

Pull request overview

This PR addresses flakiness in MCP adapter activity snapshot tests by removing nondeterministic top-level ASP.NET Core HttpRequestIn spans from captured activity roots prior to snapshotting, aligning the behavior across Diagnostics and Fusion test suites.

Changes:

• Updated McpAdapterActivityTests snapshot helper to strip top-level Microsoft.AspNetCore.Hosting.HttpRequestIn root spans before snapshotting.
• Clarified/expanded the rationale comments in both helpers and added reciprocal “keep in sync” notes.
• Regenerated affected snapshots (including NET11_0 variants) after removing the transport root span.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/HotChocolate/Fusion/test/Fusion.Diagnostics.Tests/FusionMcpAdapterActivityTests.cs	Expanded explanation of why top-level transport HttpRequestIn spans are dropped and added a keep-in-sync reference.
src/HotChocolate/Diagnostics/test/Diagnostics.Tests/McpAdapterActivityTests.cs	Implemented pre-snapshot filtering to remove top-level HttpRequestIn roots; retained session-id scrubbing.
src/HotChocolate/Diagnostics/test/Diagnostics.Tests/snapshots/McpAdapterActivityTests.Mcp_GetPrompt.snap	Updated snapshot output after dropping the transport root span.
src/HotChocolate/Diagnostics/test/Diagnostics.Tests/snapshots/McpAdapterActivityTests.Mcp_GetPrompt_NET11_0.snap	Updated NET11_0 snapshot output after dropping the transport root span.
src/HotChocolate/Diagnostics/test/Diagnostics.Tests/snapshots/McpAdapterActivityTests.Mcp_CallTool.snap	Updated snapshot output after dropping the transport root span.
src/HotChocolate/Diagnostics/test/Diagnostics.Tests/snapshots/McpAdapterActivityTests.Mcp_CallTool_NET11_0.snap	Updated NET11_0 snapshot output after dropping the transport root span.
src/HotChocolate/Diagnostics/test/Diagnostics.Tests/snapshots/McpAdapterActivityTests.Mcp_CallTool_Tool_Does_Not_Exist.snap	Updated snapshot output after dropping the transport root span.
src/HotChocolate/Diagnostics/test/Diagnostics.Tests/snapshots/McpAdapterActivityTests.Mcp_CallTool_Tool_Does_Not_Exist_NET11_0.snap	Updated NET11_0 snapshot output after dropping the transport root span.
src/HotChocolate/Diagnostics/test/Diagnostics.Tests/snapshots/McpAdapterActivityTests.Mcp_CallTool_GraphQL_Field_Error.snap	Updated snapshot output after dropping the transport root span.
src/HotChocolate/Diagnostics/test/Diagnostics.Tests/snapshots/McpAdapterActivityTests.Mcp_CallTool_GraphQL_Field_Error_NET11_0.snap	Updated NET11_0 snapshot output after dropping the transport root span.
src/HotChocolate/Diagnostics/test/Diagnostics.Tests/snapshots/McpAdapterActivityTests.Mcp_CallTool_Field_Does_Not_Exist.snap	Updated snapshot output after dropping the transport root span.
src/HotChocolate/Diagnostics/test/Diagnostics.Tests/snapshots/McpAdapterActivityTests.Mcp_CallTool_Field_Does_Not_Exist_NET11_0.snap	Updated NET11_0 snapshot output after dropping the transport root span.

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