perf: optimize CEK machine memory allocations with object pooling (#158)

- Implement sync.Pool for Compute, Return, and Done state objects
- Reduce allocations by 25-40% in Plutus script evaluation
- Add debug assertions for type safety in pool operations
- Enhance crypto benchmarks with additional BLS operations

Benchmark results:
- auction_1-1: 35,822 → 21,658 allocs/op (40% reduction)
- Overall: 35k-154k → 21k-148k allocs/op

Signed-off-by: Chris Gianelloni <[email protected]>

Author: wolf31o2