tools: fix asciidoclint's silently-disabled checks and clean up the resulting spec violations

[Devansh-567]

Three of asciidoclint.py's checks were silently non-functional against the actual spec document (docs/v1/P4Runtime-Spec.adoc), and no test suite existed to catch it. CI was passing without validating the document.

Bugs Fixed

1. ContextAfterTitle / ContextSkipHeadings

   • check_line_wraps() and check_keywords() were gated on a [TITLE] sentinel line that does not exist in the spec document.
   • ContextSkipHeadings matched Markdown # headings instead of AsciiDoc = heading syntax.
   • Fix: Updated ContextAfterTitle to match the real document title (^= ...) and ContextSkipHeadings to match AsciiDoc headings (^=+).

2. check_trailing_whitespace

   • Line indexing (line[-2]) assumed a trailing \n, causing off-by-one errors on final lines lacking a newline.
   • Fix: Strips \n if present before evaluating trailing whitespace.

3. ContextSkipBlocks

   • Only recognized ~~~~-delimited blocks (0 occurrences in spec) while ignoring ---- listing blocks (216 occurrences), |=== tables (16), and [...] block attributes.
   • Fix: Added tracking for ---- listing blocks, |=== tables, and [...] block attribute lines.

Tests Added

• Created tools/test_asciidoclint.py covering 17 test cases across all fixed features (title detection, block skipping, trailing whitespace variations).
• Integrated python3 tools/test_asciidoclint.py -v into the asciidoc-lint CI job.

Spec Document Rewrapping

• Resolving linter false positives exposed 159 genuine over-length lines in docs/v1/P4Runtime-Spec.adoc.
• Rewrapped lines using a paragraph/list-aware reflow tool.
• Verified that content stripped of all whitespace is byte-for-byte identical between the original and updated files.