feat: add MOL field support in Python SDK

[862103595]

Summary

• expose DataType.MOL and FunctionType.MOL_FINGERPRINT in pymilvus
• support packing MOL scalar values on insert and decoding MOL scalar values from query/search results
• add focused tests for MOL type exposure, function schema validation, insert-path packing, result decoding, nullable scalar handling, and invalid input boundaries

Dependencies

• Depends on milvus-io/milvus-proto#554

Test plan

• PYTHONPATH=. python3 -m pytest --noconftest tests/test_types.py::TestTypes::test_mol_data_type tests/orm/test_schema.py::TestMolFunction tests/test_search_result.py::TestSearchResultExtended::test_mol tests/test_search_result.py::TestSearchResultExtended::test_get_field_data_with_mol tests/test_search_result.py::TestSearchResultExtended::test_extract_struct_field_value_with_mol tests/test_search_result.py::TestSearchResultExtended::test_null_values_all_scalar_types tests/test_client_types.py::TestFunctionType::test_function_type_values[MOL_FINGERPRINT-5] tests/test_client_entity_helper.py::TestEntityHelperExtended::test_pack_field_value_to_field_data_mol tests/test_client_entity_helper.py::TestEntityHelperExtended::test_pack_field_value_to_field_data_mol_invalid_input tests/test_client_entity_helper.py::TestEntityHelperExtended::test_entity_to_field_data_mol tests/test_client_entity_helper.py::TestEntityHelperExtended::test_entity_to_field_data_mol_invalid_input tests/test_client_entity_helper.py::TestEntityHelperExtended::test_extract_row_data_from_fields_data_v2_mol tests/test_client_entity_helper.py::TestEntityHelperExtended::test_extract_row_data_from_fields_data_mol tests/test_client_entity_helper.py::TestEntityHelperExtended::test_entity_to_field_data_nullable_mol tests/test_client_entity_helper.py::TestEntityHelperExtended::test_pack_field_value_nullable_mol_none -q -x

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[sre-ci-robot]

Welcome @862103595! It looks like this is your first PR to milvus-io/pymilvus 🎉

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.77%. Comparing base (799a53e) to head (79d9157).

Files with missing lines	Patch %	Lines
pymilvus/client/search_result.py	66.66%	2 Missing ⚠️
pymilvus/orm/schema.py	90.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3404   +/-   ##
=======================================
  Coverage   90.76%   90.77%           
=======================================
  Files          64       64           
  Lines       13887    13923   +36     
=======================================
+ Hits        12605    12639   +34     
- Misses       1282     1284    +2     

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