fix: Add no_source hint to prevent a sink-only table marked as source

[ferenc-csaky]

Key Chnages

• Introduce no_source table hint to prevent marking a sink-only table as a source, which can lead to Flink planning errors
• Improve error message in case of unbounded source failure in batch mode
• Add a DAG planner and usecase test that covers the added logic

[codecov]

Codecov Report

❌ Patch coverage is 10.52632% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 16.46%. Comparing base (ba53588) to head (57b1156).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...com/datasqrl/error/ValidationExceptionHandler.java	0.00%	7 Missing ⚠️
...n/java/com/datasqrl/planner/hint/NoSourceHint.java	0.00%	5 Missing ⚠️
.../com/datasqrl/planner/Sqrl2FlinkSQLTranslator.java	0.00%	4 Missing ⚠️
...n/java/com/datasqrl/planner/hint/PlannerHints.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2213      +/-   ##
============================================
- Coverage     16.47%   16.46%   -0.01%     
  Complexity     1034     1034              
============================================
  Files           620      622       +2     
  Lines         17941    17957      +16     
  Branches       2194     2195       +1     
============================================
+ Hits           2956     2957       +1     
- Misses        14680    14695      +15     
  Partials        305      305              

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[ferenc-csaky]

Superseded by #2218