chore: remove querytype-poc and relocate fixture

[shivasurya]

Summary

• Remove top-level test-fixtures/querytype-poc/ directory (misplaced POC fixture)
• Relocate app.py to sast-engine/test-fixtures/python/stdlib_chaining/ for consistency with existing test fixture organization
• Update test file references in stdlib_e2e_test.go and type_inference_evidence_test.go
• Remove unused rules.py

Test plan

• TestStdlibReturnTypeChaining_EndToEnd passes with new fixture path
• TestTypeInference_StdlibChaining passes with new fixture path
• TestTypeInference_ThirdPartyChaining skips as expected

[safedep]

SafeDep Report Summary

No dependency changes detected. Nothing to scan.

_{This report is generated by SafeDep Github App}

[github-actions]

Code Pathfinder Security Scan

No security issues detected.

Metric	Value
Files Scanned	3
Rules	38

---

_{Powered by Code Pathfinder}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.84%. Comparing base (01f0ab8) to head (95bcf45).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #604      +/-   ##
==========================================
- Coverage   83.85%   83.84%   -0.01%     
==========================================
  Files         155      155              
  Lines       20936    20936              
==========================================
- Hits        17555    17554       -1     
- Misses       2736     2739       +3     
+ Partials      645      643       -2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.