cmd(feat[trim]): Add per-command trim opt-in; tidy doctests

why: With run() verbatim by default, command methods return output
with a trailing newline. Forwarding a `trim` flag lets callers opt
into the bare value, and lets doctests show clean output without
raw-string newline noise.

what:
- Forward a `trim` parameter from git/hg/svn command methods to run().
- Use `trim=True` in command doctests and drop the trailing newline.
- Restore plain docstrings where the escaped newline is gone.

Author: tony