[FLINK-40322][python] Fix Array/Multiset from_sql_type to decode elements

[nikolauspschuetz]

Summary

ArrayType and MultisetType were calling to_sql_type on elements in from_sql_type, which is the wrong direction. This caused decoding of ARRAY and MULTISET to fail with AttributeError: 'int' object has no attribute 'toordinal'.

Fixed by calling from_sql_type instead (matching MapType.from_sql_type behavior).

Brief change log

• Add: test_array_from_sql_type_converts_elements
• Add: test_multiset_from_sql_type_converts_elements
• Fix: ArrayType.from_sql_type to decode elements via from_sql_type
• Fix: MultisetType.from_sql_type to decode elements via from_sql_type

Verifying this change

• Added tests that verify the fix (test suite will pass on CI)
• Related to existing test for MapType.from_sql_type consistency
• Regression tests for ARRAY and MULTISET

Was generative AI tooling used to co-author this PR?

[x] Yes (Claude Code (Opus 4.8))

Generated-by: Claude Code (Opus 4.8)

[flinkbot]

CI report:

• e72257f Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build