Perf: Add transaction simulation cache for common pool operations

[devdianax]

Context

Transaction simulations (preview deposit, preview borrow) are recomputed on every call with no caching.

Current Limitation/Problem

Each simulation query recomputes state from scratch. Identical simulations within same block waste compute.

Expected Outcome

Block-scoped simulation cache that reuses results for identical simulation parameters within the same block.

Acceptance Criteria

• Cache key: (operation, pool, user, asset, amount) hashed
• Cache scope: single block, cleared on new block
• Read path: check cache before computing simulation
• Write-through: update cache as operations execute
• Cache size limit: LRU eviction for large caches
• Gas savings: identical simulation in same block uses cached result
• Integration with frontend: batch simulation requests for position preview

Technical Scope

• contracts/lending-pool/src/simulation_cache.rs - simulation cache
• Frontend integration for batch simulations
• Gas benchmark: cached vs uncached simulation
• Edge cases: cache poisoning, state change mid-block invalidation