fix: normalize Binance feed symbol case

[Anikesh348]

Summary

• normalize Binance feed symbols before cached ticker lookup and subscription matching
• add regression coverage for lowercase fetchTicker and watchTicker inputs

Verification

• node node_modules/jest/bin/jest.js --config core/jest.config.js core/test/unit/dataFeeds.core.test.ts --runInBand (5 tests passed)
• node node_modules/typescript/bin/tsc --project core/tsconfig.json --noEmit
• git diff --check

Limitations

• I did not run the full monorepo test suite; validation was scoped to the affected core feed tests and the complete core TypeScript compile check.

Closes #2415