Spec/Tables: Implement Automatic Header Promotion, Shorthand Options & Cell Styles

[webmaven]

Description

Enhance table parsing and ASG generation to support automatic header row promotion (when a blank line follows the first row), table options shorthand (%header, %footer, %autowidth), and inline cell style specifiers.

Specification & ASG Requirements

• Header Promotion:
  • In AsciiDoc, if an empty line immediately follows the first row of a table (and cols does not override), the first row is promoted to a header row.
• Table Options:
  • Support shorthand [%header%footer%autowidth] and formal [options="header,footer"].
• Cell Formatting & Alignment:
  • Ensure cell style specifiers (a AsciiDoc, e emphasis, s strong, l literal, m monospace, h header, d default) cleanly nest within TableCell ASG nodes.

Proposed Changes

• Tests (TDD):
  • Add local TCK fixtures under tests/tck_harness/tests/block/table/.
  • Add unit tests in tests/test_blocks_parsing.py.
• Grammar & Transformer:
  • Update table parsing in src/asciidoctrine/transformers/block_transformer.py to handle header row detection and cell format propagation.
• Nodes & Backend:
  • Update Table, TableRow, and TableCell in nodes.py and DocutilsRenderer.visit_table in docutils_backend.py.