fix: first table chunk preserve col/row span (#4343)
### Summary
When a `Table` element was split into multiple `TableChunk`s, the
**first** chunk lost `colspan` / `rowspan` on its header
cells while continuation chunks kept them — producing inconsistent
merged-cell structure across a single split table.
Root cause: `HtmlTable.from_html_text` calls `e.attrib.clear()` on every
descendant during compactification, intending to drop
cosmetic attributes (`border`, `class`, `style`, …). That also wiped
`colspan`/`rowspan`. Continuation chunks escaped the bug
because their repeated headers come from `source_row_htmls` captured
*before* the strip; the first chunk's rows flow through
the compactified tree directly.
### Fix
Preserve `colspan` and `rowspan` through the `attrib.clear()` step in
`unstructured/common/html_table.py`. They're structural,
not cosmetic, and the rest of the chunking pipeline then carries them
through unchanged.
### Tests
-
`test_html_table.py::but_it_preserves_colspan_and_rowspan_as_structural_cell_attributes`
— unit guarantee that
compactification keeps the two span attributes and still strips
`class`/`style`/`id`/`data-*`.
-
`test_base.py::and_it_preserves_colspan_and_rowspan_in_the_first_chunk_header_rows`
— end-to-end regression: the first
`TableChunk` of a split table keeps `colspan`/`rowspan` on header cells,
matching continuation chunks.
Both tests fail on `main` and pass with this change.
<!-- CURSOR_SUMMARY -->
---
> [!NOTE]
> **Low Risk**
> Low risk, localized change to table HTML normalization that only
preserves two structural attributes; main impact is on downstream
`TableChunk` HTML fidelity for merged headers.
>
> **Overview**
> Fixes a regression where `HtmlTable.from_html_text()` compactification
stripped structural `colspan`/`rowspan`, causing the *first* chunk of a
split table to lose merged-header layout while continuation chunks
retained it.
>
> Updates the attribute-stripping step to preserve `colspan` and
`rowspan`, adds unit + end-to-end chunking regression tests to assert
consistent header spans across chunks, and bumps the release to
`0.22.23` with a changelog entry.
>
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
5463e776ce02a269db84713431280375cc092cc8. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->
