Replaces os.path/open()/os.stat()/os.chmod() calls with their Path
method equivalents across src, tests, misc, and bin, wrapping str
variables in Path(...) where they must stay str for other uses (e.g.
subprocess argv, CLI-arg formatting). helpers.safe_symlink() now
decodes StrOrBytesPath to a str Path via os.fsdecode() upfront, same
pattern already used elsewhere for the str|bytes union.
089f46690a