[SPARK-58575][PYTHON] Inline redundant error_class parameter in worker.py verify helpers

[Yicong-Huang]

What changes were proposed in this pull request?

This is a follow-up to SPARK-58529, which consolidated the row-count verification helpers in python/pyspark/worker.py but left two of them over-parameterized with an error_class argument that is always passed the same constant. This PR inlines the constant and drops the parameter:

• verify_output_row_limit: both call sites (SQL_SCALAR_ARROW_ITER_UDF and SQL_SCALAR_PANDAS_ITER_UDF) pass error_class="OUTPUT_EXCEEDS_INPUT_ROWS". The constant is inlined into the raise and the parameter is removed from the signature and both call sites.
• verify_iterator_exhausted: both call sites pass error_class="INPUT_NOT_FULLY_CONSUMED". Same treatment.

Both error classes are semantically bound to these two helpers, which together enforce the iterator-UDF contract that the number of output rows equals the number of input rows. No other code path can reuse them: for example, UDTFs have no such contract (one input row may produce many output rows) and use a different set of verifiers, so parameterizing the error class buys no reuse.

Why are the changes needed?

Addresses a non-blocking review comment on SPARK-58529. Removing the always-constant parameter makes the helpers read more clearly: the helper name states the contract and the inlined error class is the fixed violation signal, with no indirection to trace through.

Does this PR introduce any user-facing change?

No. The raised error class and message are unchanged, so there is no behavior change, no error-conditions.json change, and no change to existing test assertions.

How was this patch tested?

Existing test ScalarPandasUDFTests.test_vectorized_udf_invalid_length already exercises the INPUT_NOT_FULLY_CONSUMED path through verify_iterator_exhausted. This PR additionally adds a case to that test covering an iterator UDF that emits more output rows than input rows, which exercises the OUTPUT_EXCEEDS_INPUT_ROWS fail-fast path through verify_output_row_limit (previously untested).

Was this patch authored or co-authored using generative AI tooling?

No.