Fixes #8680.

You can now do coder stat disk /some/path as well as coder stat disk --path /some/path.
You can also, confusingly, also do coder stat disk --path /some/path /some/other/path, in which case the positional arg /some/other/path will take precedence.

Changing this behaviour (i.e. making path a required arg for this command) would be breaking, so preserving existing behaviour.

Additionally, statting a nonexistent path now looks somewhat nicer:

coder stat disk /foo
running command "coder stat disk": not found: "/foo"