remove promisfy

[stefangutica]

Reasoning

• Eliminate Node DEP0174 warning
• Modernize multi.exec usage
• Keep metrics timing reliable

Proposed Changes

• Replace promisify(multi.exec) with await multi.exec()
• Record MULTI metric in finally
• Small, localized change in redis-cache.service.ts

How to test

• Run cache tests: cd packages/cache && npm test
• Trigger bulk cache ops (e.g. setMany, deleteByPattern)
• Verify no DEP0174 warning and MULTI metric logged