Add Flink config validation warnings

[velo]

Summary

• Adds FlinkConfigValidator that validates engines.flink.config entries at compile time with 3 levels of checks:
  • Misplacement detection: warns when deployment-only keys (taskmanager-size, jobmanager-size, etc.) are placed in config instead of deployment
  • Unknown key detection with prefix awareness: scans Flink *Options classes via reflection to build known keys/prefixes; warns on unrecognized keys with extra hint when the prefix is valid (likely typo)
  • Value type validation: checks Boolean, Integer, Long, Duration, and MemorySize values against expected types
• All checks emit warnings (not errors) via ErrorCollector.warn() so compilation is never blocked
• Injects ErrorCollector into FlinkStreamEngine constructor to run validation on startup

Test plan

• FlinkConfigValidatorTest — 11 test cases covering all validation levels and edge cases
• All sqrl-planner tests pass (184/184, 0 failures)

🤖 Generated with Claude Code

[velo]

Original idea came from slack
https://datasqrl.slack.com/archives/C09AQ9RUYH1/p1771005181650889?thread_ts=1770829996.213029&cid=C09AQ9RUYH1

[codecov]

Codecov Report

❌ Patch coverage is 83.75000% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 13.55%. Comparing base (13863c4) to head (2787654).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...sqrl/engine/stream/flink/FlinkConfigValidator.java	84.81%	8 Missing and 4 partials ⚠️
...atasqrl/engine/stream/flink/FlinkStreamEngine.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1865      +/-   ##
============================================
+ Coverage     13.14%   13.55%   +0.40%     
- Complexity      742      774      +32     
============================================
  Files           550      551       +1     
  Lines         16137    16217      +80     
  Branches       1896     1915      +19     
============================================
+ Hits           2122     2199      +77     
+ Misses        13817    13816       -1     
- Partials        198      202       +4     

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