* test(#2366): regression tests for parseCoverageMatrix scoping bugs
Bug 1: summary table outside matrix not parsed as data
Bug 2: multi-section matrix with repeated headers parses correctly
Bug 3: markdown emphasis on decision cell is stripped
* fix(#2366): scope parseCoverageMatrix to recognized coverage tables
Replace latching sawHeader with contextual inMatrix tracking that
resets on non-pipe lines, preventing summary tables from being parsed
as data (bug 1). Allow multiple headers for multi-section matrices
(bug 2). Strip markdown emphasis from decision cells before validation
(bug 3).
Closes#2366
* fix(#2366): update representative-corpus test to expect correct behavior
The test previously documented the known-buggy parseCoverageMatrix behavior.
Now that the fix is in place, test against the expected correct output
(expectedBlock, expectedCounts, expectedErrorCount) instead of the
currentBuggyOutput snapshot.
* docs(#2366): backfill changeset PR number (2551)
