Feat: add governance lifecycle benchmark suite

[rian-be]

Summary

This PR expands governance benchmark coverage by splitting the lifecycle suite into dedicated submission, transition, and expiration benchmarks.

Highlights

Submission benchmarks

• Measure pending request submission into the governance lifecycle.
• Keep lifecycle submission setup local to the benchmark project.

Transition benchmarks

• Measure approve, reject, and cancel lifecycle transitions.
• Keep terminal lifecycle costs visible in isolation from approval workflow internals.

Expiration benchmarks

• Measure expiration sweeps for pending governance requests.
• Keep expiration behavior separate from approval-specific expiration paths.

Why

Issue #76 asks for benchmark visibility into request submission, approval related lifecycle transitions, expiration, and cancellation.

Splitting the suite keeps each lifecycle path focused and makes the benchmark outputs easier to read and extend.

Checks

• dotnet build Benchmarks/ModularityKit.Mutator.Benchmarks.csproj -c Release

Closes

• Closes [Benchmark]: Measure governance request lifecycle #76
• Closes [Benchmark]: Measure governance approval workflow #75