feat: Support defining sort order in index hints

[ferenc-csaky]

Summary

Adds sort-order support for JDBC index hints and propagates Calcite sort direction into generated B-tree index candidates.

Key Changes

• Supports index hints such as /*+ index(BTREE, col_a DESC, col_b) */.
• Adds index-column directions to IndexDefinition.
• Adds sort metadata to QueryIndexSummary.
• Preserves Calcite RelFieldCollation.Direction when selecting indexes for limited sorted queries.
• Generates distinct index names for descending columns.
• Emits DESC in PostgreSQL CREATE INDEX DDL.
• Adds IndexType.supportsSortOrder() to centralize index capability checks.
• Rejects descending columns for index types that do not support sort order.
• Adds parser, index-selector, and PostgreSQL DDL tests.

[codecov]

Codecov Report

❌ Patch coverage is 35.78947% with 61 lines in your changes missing coverage. Please review.
✅ Project coverage is 19.04%. Comparing base (d4123f8) to head (9365c48).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...n/java/com/datasqrl/plan/global/IndexSelector.java	0.00%	18 Missing ⚠️
...va/com/datasqrl/plan/global/QueryIndexSummary.java	7.14%	12 Missing and 1 partial ⚠️
...engine/database/relational/ddl/CreateIndexDDL.java	0.00%	8 Missing ⚠️
...java/com/datasqrl/plan/global/IndexDefinition.java	55.55%	7 Missing and 1 partial ⚠️
...main/java/com/datasqrl/planner/hint/IndexHint.java	76.66%	4 Missing and 3 partials ⚠️
.../database/relational/PostgresStatementFactory.java	0.00%	6 Missing ⚠️
.../main/java/com/datasqrl/plan/global/IndexType.java	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2246      +/-   ##
============================================
+ Coverage     18.28%   19.04%   +0.75%     
- Complexity     1133     1169      +36     
============================================
  Files           612      612              
  Lines         17828    17882      +54     
  Branches       2175     2183       +8     
============================================
+ Hits           3260     3405     +145     
+ Misses        14246    14129     -117     
- Partials        322      348      +26     

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