The ripgrep/grep output parser uses `split(':', 2)` to extract
file:lineno:content from match lines. On Windows, absolute paths
contain a drive letter colon (e.g. `C:\Users\foo\bar.py:42:content`),
so `split(':', 2)` produces `["C", "\Users\...", "42:content"]`.
`int(parts[1])` then raises ValueError and the match is silently
dropped. All search results are lost on Windows.
Same category as #390 — string-based path parsing that fails on
Windows. Replace `split()` with a regex that optionally captures
the drive letter prefix: `^([A-Za-z]:)?(.*?):(\d+):(.*)$`.
Applied to both `_search_with_rg` and `_search_with_grep`.
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