term: render Markdown tables without wrapping rows

[fzlzjerry]

Closes #11175

Markdown tables are now parsed into separate blocks instead of being flattened into the same wrapping Paragraph as surrounding prose. Table blocks reuse the helix-tui table widget, preserve Markdown column alignment, style separators with punctuation.special, and truncate cells when the popup is narrower than the table.

This follows the rendering direction discussed in #12693. The table widget gains aligned cells, styled column separators, compressed-gap handling for narrow areas, and correct offset behavior when there is no selected row. Hover and signature-help sizing and scrolling now use the block-aware Markdown renderer.

Tests cover table parsing and alignment, normal and narrow rendering, compressed separators, unselected table offsets, and scrolling from a table into following Markdown blocks.

Validation:

• cargo fmt --all -- --check
• cargo test -p helix-tui
• HELIX_DISABLE_AUTO_GRAMMAR_BUILD=1 cargo test -p helix-term --lib
• HELIX_DISABLE_AUTO_GRAMMAR_BUILD=1 cargo clippy -p helix-tui -p helix-term --all-targets -- -D warnings
• HELIX_DISABLE_AUTO_GRAMMAR_BUILD=1 RUSTDOCFLAGS="-D warnings" cargo doc --no-deps -p helix-tui -p helix-term --document-private-items

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