Benchmark voting-snapshot worst-case EndBlock behavior

[juno-ai-dev]

Scope

Add deterministic benchmarks for slash/status processing with mainnet-shaped validators, including more than 10,000 delegators.

Acceptance criteria

• Deterministic fixtures.
• CPU, allocations, and iteration counts for representative sizes.
• Same-block voting-power correctness asserted.
• Explicit RC performance threshold.
• Only optimize if evidence exceeds threshold; any strategy remains bounded and regression-tested.