Summary

This PR expands benchmark coverage for ModularityKit.Mutator by adding dedicated engine throughput and policy evaluation suites, then reorganizes the benchmark project into scenario-focused folders.

Highlights

Core engine throughput benchmarks

• Add dedicated engine benchmarks under Benchmarks/Engine.
• Measure single mutation throughput separately from batch throughput.
• Compare throughput across explicit StateSize and BatchSize parameters.
• Split commit, mode, batch, and throughput scenarios into focused benchmark classes.

Policy evaluation benchmarks

• Add dedicated policy benchmarks under Benchmarks/Policy.
• Measure no policy baseline, single synchronous policy, single asynchronous policy, and mixed multi policy evaluation paths.
• Keep helper mutations and policies local to the benchmark project.

Benchmark project structure

• Replace the previous all-in-one engine benchmark class with smaller concern-specific classes.
• Add support helpers scoped to Engine and Policy folders.
• Update namespaces and XML docs to match the physical benchmark layout.
• Refresh Benchmarks/README.md with the new benchmark filters and suite descriptions.

Why

Issue #56 asks for throughput focused visibility into the core mutation runtime across single and batch execution paths, including meaningful state size variation.

Issue #57 asks for explicit policy overhead benchmarks across sync, async, and multi-policy execution modes.

This PR addresses both issues while cleaning up the benchmark project structure so the suite is easier to extend and compare over time.

Checks

• dotnet build Benchmarks/ModularityKit.Mutator.Benchmarks.csproj -c Release
• sample local BenchmarkDotNet runs for engine throughput and policy evaluation scenarios

Closes

• Closes [Benchmark]: Measure mutation engine throughput #56
• Closes [Benchmark]: Measure policy evaluation overhead #57