Fix 671 pre-existing mypy type errors

[anchapin]

Summary

The codebase has 671 mypy type checking errors that are pre-existing in the main branch. These errors are blocking the CI Type Check job.

Current Status

• Lint: ✅ Passing
• Type Check: ❌ 671 errors
• E2E Tests: ✅ Passing
• Security Scan: ✅ Passing

Error Categories

The main categories of errors include:

1. Invalid base class "Base" - Many SQLAlchemy models have issues with not being recognized as a valid type (valid-type, misc errors)
2. Union attribute errors - Optional types having None checks but still accessed without proper handling (union-attr)
3. Name redefinitions - Properties defined multiple times (no-redef)
4. Missing type stubs - Third-party libraries without type stubs (import-untyped)
5. Assignment type mismatches - Incompatible types in assignment (assignment)

Files with Most Errors

• • Multiple Base class issues
• • Multiple Base class issues
• • Multiple issues
• • Base class issues
• • Base class issues
• • Union attribute errors
• • Type assignment issues
• • Missing stubs and type issues

Recommendation

These errors have likely accumulated over time and should be addressed systematically. Options include:

1. Fix incrementally - Address errors file by file
2. Add to ignore list - Add pre-existing errors to mypy ignore list in pyproject.toml (like we did for lint)
3. Enable strict mode gradually - Consider enabling stricter mypy settings incrementally

Verification

Run locally with:

mypy src/ --config-file=pyproject.toml

See CI run for current status: https://github.com/anchapin/ArbitrageAI/actions/runs/22770689934

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