perf(backend): add escrow query performance indexes

[pchieneye]

perf(backend): add database indexing for escrow query performance

This PR adds database indexes for the most common escrow lookup patterns to improve query performance as the dataset grows.

What changed

• Added an index on escrow status for status-based filtering
• Added a composite index on creator and status for the common filtered lookup pattern
• Added indexes on escrow creation and expiry timestamps for date-range and expiry queries
• Added a wallet-address index for wallet-based party/user lookups
• Added an index on escrow event escrow IDs for event retrieval queries
• Added a migration file covering all requested indexes
• Added a regression test to validate the migration creates the expected indexes

Testing

• Verified the migration includes all requested index creation statements
• Added a regression test for the new migration

Closes: #486

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[KuchiMercy]

@pchieneye, kindly resolve the error. Thanks