IMPALA-15157: Avoid decompressing a page that is fully skipped at a page boundary

During late materialization / row-level skipping, when the rows to skip
end exactly on a Parquet page boundary (e.g. an entire row group is
filtered out by row-level predicates), BaseScalarColumnReader::
SkipRowsInternal() would fall out of the page-skipping loop and then
decompress that final page via ReadCurrentDataPage() only to then skip
all of its values.

This changes the loop guard from '>' to '>=' so a page whose values are
all skipped is discarded as a whole compressed page (counted in
NumPagesSkippedByLateMaterialization) without decompressing it. When the
skip lands exactly on the page boundary we short-circuit and return
before reading the next page header. Query results are unchanged; this
only removes the unnecessary decompression and in-page value skipping.

Testing:
- Updated and extended parquet-late-materialization-unique-db.test to
  cover skipping to a page boundary (whole-page discard) and in-page
  value skipping.

Assisted-by: Claude Opus 4.8
Change-Id: I18f0e69c267c9bf041ff9f6a3d677239ae43971a
Reviewed-on: http://gerrit.cloudera.org:8080/24566
Reviewed-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>