fix: first table chunk preserve col/row span

[badGarnet]

Summary

When a Table element was split into multiple TableChunks, 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.

---

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.

^{Reviewed by Cursor Bugbot for commit 5463e77. Bugbot is set up for automated code reviews on this repo. Configure here.}