Spec/Tables: Support Data Formats (CSV / TSV / DSV) and File Data Loading

[webmaven]

Description

Support table data format specifiers (format=csv, format=tsv, format=dsv, [csv], [dsv]) and external delimited data loading in table blocks.

Specification Reference

• Spec: link:https://gitlab.eclipse.org/eclipse/asciidoc-lang/asciidoc-lang/-/blob/main/docs/modules/tables/pages/data-format.adoc[Table Data Formats]
• Syntax:
  • [format=csv,options=header] or [%header,csv] with comma/tab/colon delimited content.
  • Integration with include::data.csv[] inside table blocks.

Proposed Changes

• Tests (TDD):
  • Add unit tests in tests/test_blocks_parsing.py and tests/test_tables.py.
  • Add local TCK fixtures under tests/tck_harness/tests/block/table/.
• Implementation:
  • In src/asciidoctrine/transformers/block_transformer.py, detect data format attribute on tables and parse delimited cell lines into TableRow and TableCell AST nodes using Python's csv module / delimiter parser.
  • Update docutils_backend.py to render formatted data tables.