Add Fusion result-composition hot path micro benchmarks

[michaelstaib]

No description provided.

[Copilot]

Pull request overview

Adds a set of BenchmarkDotNet microbenchmarks focused on Fusion execution “result composition” hot paths, intended to quantify candidate micro-optimizations (string transcoding avoidance, selection-set lookup flattening, MetaDb row reads, row reuse, templated object row writes, and abstract type resolution memoization).

Changes:

• Added benchmark for hoisting UTF-8 transcoding of source-path segments during per-result JSON document walks.
• Added benchmarks for selection set child lookup, MetaDb row reads, enum/scalar list element completion row reuse, and templated object row materialization.
• Added benchmark for memoizing abstract type resolution based on __typename bytes to avoid allocations/lookups on homogeneous lists.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/HotChocolate/Fusion/benchmarks/Fusion.Execution.Benchmarks/SourcePathTranscodeHoistBenchmark.cs	Benchmarks per-result source-path walking with per-segment string transcode vs hoisted UTF-8 segment bytes.
src/HotChocolate/Fusion/benchmarks/Fusion.Execution.Benchmarks/ResultSelectionSetLookupBenchmark.cs	Benchmarks current ResultSelectionSet.TryGetChild vs a benchmark-local flattened sealed implementation.
src/HotChocolate/Fusion/benchmarks/Fusion.Execution.Benchmarks/MetaDbGetBenchmark.cs	Benchmarks MetaDb row reads via product API vs local span-read copy vs GetArrayDataReference + Unsafe.ReadUnaligned.
src/HotChocolate/Fusion/benchmarks/Fusion.Execution.Benchmarks/EnumScalarRowReuseBenchmark.cs	Benchmarks repeated row decode vs single-decode row reuse for enum/scalar list element completion.
src/HotChocolate/Fusion/benchmarks/Fusion.Execution.Benchmarks/CompositeObjectCreateTemplateBenchmark.cs	Benchmarks per-row append loop vs template block-copy + parent stamping for composite object row creation.
src/HotChocolate/Fusion/benchmarks/Fusion.Execution.Benchmarks/AbstractTypeResolutionMemoBenchmark.cs	Benchmarks baseline abstract type resolution vs 1-entry and 2-entry MRU memoization using raw UTF-8 type names.

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