[Parquet] Add ALP regression coverage for an empty first page

### Describe the bug

Add regression coverage for encoding a column chunk whose first data page is empty or contains only nulls, followed by a page containing values.

See [@alamb's comment](https://github.com/apache/arrow-rs/pull/9372#issuecomment-5217749936) and [@devanbenz's suggested regression test](https://github.com/apache/arrow-rs/pull/9372#discussion_r3737514569).

This depends on #9372 and should be worked on after that PR is merged.

Start by reading PR #9372 and the linked comment and suggested regression-test discussion. Add coverage for a column chunk whose first data page is empty or contains only nulls, followed by a page with values, after #9372 is merged; the regression test should pass for this sequence.

Written by the indexing model from the issue text.