[FLINK] Improve table format and source reader read path test coverage

[cshuo]

Problem

Several Flink table-format and source-reader read paths have limited unit-test coverage, especially around partition path handling, CDC iteration, schema reconciliation, and COW split planning.

Scope

Add focused unit coverage for:

• partition path parsing, construction, and validation
• CDC image management and CDC log iteration
• read-time schema reconciliation and Parquet configuration
• COW input split planning and partition pruning
• record iterator lifecycle and row projection

Acceptance criteria

• Add small, deterministic unit tests for the targeted read paths
• Verify the targeted Flink tests pass
• Run the tests with JaCoCo enabled to confirm the exercised lines are reported