feat: add configurable memory-limit for DuckDB engine

[WellMafra]

Summary

• Added memory-limit field to JdbcConfig.DuckDbConfig (JSON key memory-limit)
• DuckDbExtensions.buildInitSql() now emits SET memory_limit='<value>' before loading extensions when the field is set
• Fixed log statement: was logging null extensionDir value; now logs the env var name DUCKDB_EXTENSIONS_DIR

Usage

Configure in package.json server section:

"duckdb": {
  "url": "jdbc:duckdb:",
  "memory-limit": "20GB"
}

Without this setting, DuckDB defaults to ~80% of available system RAM — causing OOM kills when running alongside Flink in a shared pod.

Test plan

• Deploy workbench query executor with memory-limit: "20GB" configured
• Verify SELECT current_setting('memory_limit') in DuckDB returns "20.0 GiB"
• Confirm TM pods no longer OOM crash loop under workbench query load

[codecov]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 13.92%. Comparing base (7e50529) to head (3cdf7e4).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...main/java/com/datasqrl/util/DuckDbInitializer.java	0.00%	9 Missing ⚠️
...a/com/datasqrl/graphql/jdbc/JdbcClientsConfig.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2059      +/-   ##
============================================
- Coverage     13.92%   13.92%   -0.01%     
  Complexity      854      854              
============================================
  Files           604      604              
  Lines         17246    17251       +5     
  Branches       2085     2086       +1     
============================================
  Hits           2402     2402              
- Misses        14612    14617       +5     
  Partials        232      232              

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