[Fusion] Reduce per request allocations

[michaelstaib]

No description provided.

[Copilot]

Pull request overview

This PR focuses on reducing per-request allocations in Fusion execution by replacing temporary collections with pooled buffers and tighter data structures.

Changes:

• Replace Path.ToList()-based segment materialization with ArrayPool-backed buffers and a new Path.CopyTo(Span<object>) API.
• Pool VariableValues[] allocations in FetchResultStore and copy out the final immutable result.
• Reduce runtime overhead in execution state tracking (bitset instead of HashSet<int>) and avoid repeated schema name computation during subscription event processing.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
src/HotChocolate/Fusion/src/Fusion.Execution/Execution/Results/PathUtilities.cs	Uses pooled object[] buffers to compare path segments without allocating lists.
src/HotChocolate/Fusion/src/Fusion.Execution/Execution/Results/FetchResultStore.cs	Uses pooled buffers for path traversal and variable value set construction/finalization.
src/HotChocolate/Fusion/src/Fusion.Execution/Execution/OperationPlanExecutor.cs	Caches schemaName once for subscription event diagnostics.
src/HotChocolate/Fusion/src/Fusion.Execution/Execution/OperationPlanContext.Pooling.cs	Ensures pooled execution state resources are released on context destruction.
src/HotChocolate/Fusion/src/Fusion.Execution/Execution/OperationPlanContext.cs	Reduces allocations when materializing skipped definitions and forwarded variable field nodes.
src/HotChocolate/Fusion/src/Fusion.Execution/Execution/ExecutionState.cs	Replaces skipped/failed tracking with a pooled bitset and pools internal arrays.
src/HotChocolate/Fusion/src/Fusion.Execution/Execution/Clients/SourceSchemaErrors.cs	Switches to Path.CopyTo and reuses a cached shared ArrayPool<object>.
src/HotChocolate/Core/src/Execution.Abstractions/Path.cs	Renames span-based path materialization to CopyTo(Span<object>) and updates docs.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (d68df74) to head (2de82db).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

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##   main   #9512   +/-   ##
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