Implements `kb_parse_md::parse_blocks(body, body_offset_lines)` returning a
flat `Vec<ParsedBlock>` plus warnings. Walks pulldown-cmark events through a
small frame-based state machine that tracks heading paths, accumulates
inline buffers (Text/Code/Link/Strong/Emph only — design §3.4), and
reports SourceSpan::Line spans in 1-indexed file-line coordinates.
Covers headings, paragraphs, code blocks (lang from info string), GFM
tables (with malformed fallback to paragraph + MalformedTable warning),
lists (nested sub-lists flattened into parent item), and block-level image
references. Inline images are dropped silently per the inline filter.
Adversarial inputs are caught with `catch_unwind` and degrade to an empty
output + ExtractFailed warning.
15 unit tests cover heading-path correctness, code lang, table parsing,
malformed-table fallback (driven via synthetic events since pulldown-cmark
auto-normalizes table widths), LF/CRLF line-range parity, image refs,
nested-list flattening, inline filter, and 100-iteration random-bytes plus
hand-crafted adversarial-input no-panic guards.