fix(xlsx): XLSX emits std minified .text_as_html

[scanny]

Summary Eliminate historical "idiosyncracies" of table.metadata.text_as_html HTML introduced by partition_xlsx(). Produce minified .text_as_html consistent with that formed by chunking.

Additional Context

• XLSX .text_as_html is minified (no extra whitespace or thead, tbody, tfoot elements).
• table.text is clean-concatenated-text (CCT) of table.