[improvement](fe) Route small MaxCompute limit scans through MCQA

### What problem does this PR solve?

Issue Number: None

Related PR: None

Problem Summary: Route non-partition-table select-star limit queries and partition-filtered select-star limit queries to MaxCompute MCQA, while keeping larger limits on the existing split logic through a new catalog threshold.

### Release note

Small MaxCompute SELECT * LIMIT queries can use MCQA when the limit is below the catalog threshold.

### Check List (For Author)

- Test: Unit Test
    - Unit Test: ./run-fe-ut.sh --run org.apache.doris.datasource.maxcompute.source.MaxComputeScanNodeTest
- Behavior changed: Yes
- Does this need documentation: No

Constraint: MaxCompute MCQA should only target low-limit select-star scans and fall back to existing split planning for larger limits
Rejected: Reuse the existing limit split optimization switch for MCQA gating | it does not express catalog-level MCQA routing limits
Confidence: medium
Scope-risk: moderate
Reversibility: clean
Directive: Keep partitioned-table MCQA routing limited to partition-filtered select-star queries unless scanner contract tests are added
Tested: ./run-fe-ut.sh --run org.apache.doris.datasource.maxcompute.source.MaxComputeScanNodeTest
Not-tested: max-compute-connector module compile and end-to-end MCQA scanner execution; blocked by Maven repository and dependency environment issues

Author: hubgeter