Implement Deletes for FlatPostgresCollection

[suddendust]

PR: Implement Delete Operations for Flat PostgreSQL Collections

Methods Implemented

• delete(Key key) - Delete single document by primary key
• delete(Set keys) - Bulk delete by multiple keys
• delete(Filter filter) - Delete using legacy Filter (delegates to new API)
• deleteAll() - Delete all documents from collection

Why Deprecate delete(Filter filter)?

The legacy Filter class uses hardcoded JSONB document access patterns that don't work with flat collections where fields are direct PostgreSQL columns. The parsing logic assumes nested document structure.

Why New delete(query.Filter filter)?

The new query.Filter wraps FilterTypeExpression which:

• Works with the v1 PostgresQueryParser that supports pluggable field transformers
• Uses FlatPostgresFieldTransformer to correctly resolve field names to PostgreSQL columns
• Properly handles nested JSONB paths via JsonIdentifierExpression
• Maintains consistency with other query operations that already use this API

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.65%. Comparing base (57533ac) to head (4f62ffc).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...documentstore/postgres/FlatPostgresCollection.java	83.33%	8 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #270      +/-   ##
============================================
+ Coverage     80.63%   80.65%   +0.02%     
  Complexity     1396     1396              
============================================
  Files           240      240              
  Lines          6815     6871      +56     
  Branches        636      638       +2     
============================================
+ Hits           5495     5542      +47     
- Misses          907      914       +7     
- Partials        413      415       +2     

Flag	Coverage Δ
integration	80.65% <83.33%> (+0.02%)	⬆️
unit	53.26% <0.00%> (-0.44%)	⬇️

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