* fix(cli): overwrite stale poetry.lock backup on windows
os.rename raises FileExistsError on Windows when poetry-old.lock already
exists from a previous run, so a second `crewai update` crashed there
while POSIX silently replaced the file. Use os.replace, which overwrites
on every platform, and add a regression test.
* test(cli): add docstrings to update_crew tests
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Co-authored-by: Vidit Ostwal <110953813+Vidit-Ostwal@users.noreply.github.com>