Support chaining FindQuery filters

[lh0156]

Summary

Implements #780 by allowing FindQuery instances to accept additional filter expressions through .find().

What changed

• Adds FindQuery.find(*expressions) and returns a new query, leaving the original unchanged.
• Appends expressions to the existing query so they use the same AND semantics as Model.find(expr1, expr2).
• Preserves the query's KNN state when creating the chained query.
• Documents incremental filter construction.

Testing

• pytest -q tests/test_find_query.py tests_sync/test_find_query.py: 52 passed.
• pytest -q tests --ignore tests/test_benchmarks.py: 261 passed.
• pytest -q tests_sync --ignore tests_sync/test_benchmarks.py: 261 passed.
• ruff check and ruff format --check on changed source/tests.
• python -m compileall -q aredis_om tests.
• bandit -q -r aredis_om/model/model.py -s B608.

Redis Stack was run locally through Docker Compose for the integration tests; benchmark tests were excluded from the full run.

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Note

Low Risk
Small, additive query API on top of existing FindQuery.copy() behavior; covered by find-query tests with no auth or data-migration impact.

Overview
FindQuery now supports chaining filters via a new .find(*expressions) method, so you can build queries step by step instead of passing every predicate into Model.find() up front.

Each call returns a new FindQuery (via copy()), appending expressions with the same AND semantics as Model.find(expr1, expr2), and preserves KNN state on the chained query. Documentation in querying.md shows incremental construction; an async integration test verifies chaining, sorting, and that the original query object is unchanged.

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[abrookins]

@lh0156 This sounds great! I'll take a look ASAP.