Fix per-resolve closure allocation in resolve pipeline (#1493)

[tillig]

Fixes #1493.

Problem

@BrendanLally reported that per-resolve memory allocations increased in Autofac 9.2+ and traced it to ResolvePipelineBuilder.BuildPipeline. The diagnosis is correct.

The 9.2 "Consolidated metrics handling" refactor introduced a shared ExecuteWithDiagnostics(context, stage, Action action) helper, called like:

return context => ExecuteWithDiagnostics(context, stage, () =>
{
    context.PhaseReached = stagePhase;
    stage.Execute(context, next);
});

The inner () => { ... } lambda captures context — a per-invocation parameter — so a fresh closure is allocated for every middleware stage on every resolve. In 9.1 the equivalent lambda closed over only build-time state and was allocated once per pipeline build (pipelines are cached). BuildMetricsMiddlewareChain had the same defect.

Fix

Inline the diagnostics/metrics logic into each build-time lambda so they close only over build-time state (next, stage, stagePhase, stageName) and are allocated once per pipeline build. Both the standard and metrics-enabled chains are fixed. The two builders were extracted to static methods to keep BuildPipeline within the cognitive-complexity analyzer limit. Diagnostics and metrics behavior is unchanged.

Validation

Added ResolvePipelineAllocationBenchmark (mirroring the reported repro) and compared current source against the 9.1.0 NuGet package via the benchmark harness's baseline feature:

Scenario	NoDependencies	OneDependency
9.1.0 baseline	832 B	1336 B
9.2/9.3 (before fix)	1056 B (+224)	1784 B (+448)
After fix	832 B	1336 B

The 9.1.0 numbers match the reporter's exactly, and the fix fully restores them (the timing regression is gone too).

Tests

Added PipelineBuilderTests.InvokingBuiltPipelineDoesNotAllocatePerInvocation, asserting a built pipeline allocates zero bytes per invocation. Verified it fails on the pre-fix code (32 B/stage per resolve) and passes with the fix. Full core (870) and specification (498) suites pass; dotnet format is clean.

[codecov]

Codecov Report

❌ Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 78.24%. Comparing base (b7f65d6) to head (9b84ca8).

Files with missing lines	Patch %	Lines
.../Core/Resolving/Pipeline/ResolvePipelineBuilder.cs	94.44%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1494      +/-   ##
===========================================
+ Coverage    77.99%   78.24%   +0.24%     
===========================================
  Files          218      218              
  Lines         5945     5944       -1     
  Branches      1273     1273              
===========================================
+ Hits          4637     4651      +14     
+ Misses         768      753      -15     
  Partials       540      540              

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