What this PR does / why we need it:

SqliteFilterTranslator.translate_compound and PostgresFilterTranslator.translate_compound join every sub-clause, including the empty clause returned for an empty nested CompoundFilter. A filter such as and[eq(title, "Title 1"), or[]] becomes (... AND ), and SQLite fails with near ")": syntax error. Postgres gets the same trailing AND ). A group made only of empty groups becomes ( AND ) or ().

This change skips empty sub-clauses and returns an empty clause when none remain, which matches MilvusFilterTranslator. The callers already treat an empty clause as "no filter".

Tests in tests/unit/test_filter_models.py check the generated clause for both translators, run the SQLite clause against an in-memory database, and cover groups made only of empty groups.

Which issue(s) this PR fixes:

Fixes #7051

Checks

• I've made sure the tests are passing.
• My commits are signed off (git commit -s)
• My PR title follows conventional commits format

Testing Strategy

• Unit tests
• Integration tests
• Manual tests
• Testing is not required for this change

Misc

pytest tests/unit/test_filter_models.py: 4 of the new tests fail without the fix and all 27 pass with it.