Support empty dynamic filters

[mimimind]

Summary

• let Filter.all_of() ignore None entries and return a serializable no-op filter when no entries remain
• omit no-op filters from gRPC and REST requests, including when combined or inverted
• cover empty, all-None, mixed, and composed dynamic filters

Fixes #1092.

Validation

• test/collection/test_filter.py: 38 passed
• test/collection: 326 passed, 1 skipped
• full unit suite: 419 passed, 1 skipped; 2 unrelated Windows-only timeout-output assertion failures
• Ruff and Flake8 passed on weaviate and test
• Pyright on changed source: 0 errors

[orca-security-eu]

Orca Security Scan Summary

Status	Check	Issues by priority
Passed	Infrastructure as Code	0   0   0   0	View in Orca
Passed	SAST	0   0   0   0	View in Orca
Passed	Secrets	0   0   0   0	View in Orca
Passed	Vulnerabilities	0   0   0   0	View in Orca

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[mimimind]

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