[Enhancement] Prune trailing fields in Hive TEXTFILE split for column-pruned queries

### Search before asking

- [x] I had searched in the [issues](https://github.com/apache/doris/issues) and found no similar issues.

### Description

A column-pruned Hive `TEXTFILE` query reads only the columns listed in `_col_idxs`, but the field splitter still scans every separator of each line — including trailing fields that are never used. For wide tables with many unused trailing columns this is wasted work proportional to the unused tail length of every row.

### Proposal

On the query path, after the reader resolves `_col_idxs`, compute `max(_col_idxs) + 1` and pass it to the splitter as a split limit. The single-char, non-escape path of `HiveTextFieldSplitter` then stops as soon as it has emitted that many fields. Each emitted field is still bounded by its own separator, so the produced prefix is byte-identical to a full split, and the reader only needs those prefix columns — query results are unchanged.

The escape-configured path, the multi-char (KMP) path, and `EncloseCsvTextFieldSplitter` ignore the limit and split fully, so escaped separators and enclose quoting are unaffected. The load path is unaffected.

### Use case

Faster scans of wide Hive `TEXTFILE` tables when queries select only a prefix of the columns.

### Related issues

_No response_

### Are you willing to submit PR?

- [x] Yes I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)

Start by locating HiveTextFieldSplitter and the reader path that resolves _col_idxs. Compare the single-character, non-escape path with the escape, multi-character, and enclose paths, then run the relevant existing tests or add coverage to verify prefix output and unchanged query results.

Written by the indexing model from the issue text.