fix(python): validate query topk

[HosniBelfeki]

Summary

Validate Collection.query(topk=...) before building the query context.

The Python wrapper already has _require_positive_integer() for group-by limits, but plain query() passed invalid topk values through to the executor/native layer. This change rejects 0, negative values, None, and booleans with a clear Python-side ValueError.

Tests

• python -m ruff check python\zvec\model\collection.py python\tests\test_collection.py
• python -m py_compile python\zvec\model\collection.py python\tests\test_collection.py

[Copilot]

Pull request overview

Adds Python-side validation for Collection.query(topk=...) to reject invalid values early (before query context construction / native execution), aligning query() behavior with existing group-by limit validation.

Changes:

• Validate topk via _require_positive_integer(topk, "topk") at the start of Collection.query().
• Add a unit test to ensure invalid topk values raise a clear ValueError and do not call the executor.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
python/zvec/model/collection.py	Adds _require_positive_integer check for topk in Collection.query() before building QueryContext.
python/tests/test_collection.py	Adds parametrized test covering invalid topk values and asserts the executor is not invoked.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.