Merge branch 'mm/test-grep-lint'

The test suite has been updated to use the 'test_grep' helper instead of bare 'grep' for test assertions, allowing file contents to be printed on failure for easier debugging. A new 'greplint' linter has been introduced to detect and prevent new bare 'grep' assertions from being added to the test suite. * mm/test-grep-lint: t: add greplint to detect bare grep assertions t: convert grep assertions to test_grep t: fix Lexer line count for $() inside double-quoted strings t: extract chainlint's parser into shared module t: fix grep assertions missing file arguments t/README: document test_grep helper