Fix ripgrep output parsing on Windows drive-letter paths

[harshdotcom]

What

Fixes the grep tool returning corrupted results on Windows when ripgrep is installed.

_parse_rg split each ripgrep output line with line.split(":", 2). ripgrep is
invoked with an absolute search path, which on Windows starts with a drive
letter (C:\...) — that colon was mistaken for the path:line:text field
separator, so every match reported file "C", line 0, with the real line
number leaked into the text field.

Fix

Anchor the parse on the numeric :<line>: field with a regex
((.+?):(\d+):(.*)), so both the drive-letter colon and any colons inside the
matched text are preserved. A plain rsplit(":", 2) would not work — matched
text frequently contains colons (e.g. def hello():).

Testing

• Added test_parse_rg_handles_windows_drive_letter_and_colons_in_text
  (platform-independent — hardcodes a Windows-style line). It fails on the old
  split(":", 2) and passes on the fix.
• Full grep suite passes.

Closes #17

[rohitprasad15]

Thanks — you were the first to catch the Windows drive-letter parsing bug, and your fix was correct for the main case. We merged #123, which fixes the emission side instead (--with-filename --null), which also covers colons in filenames and the single-file case where rg omits the filename. Windows grep is now fixed on main, so I'm closing this one. Appreciate the report and fix!