Previously a number of subcommands dumped the entire `nvm --help`
output (~100 lines) when arguments were missing or invalid,
drowning the real error.
Replace each dump with a short,
command-specific usage block that names the expected syntax and points to `nvm --help` for full help.
The exit code (127) is unchanged.
Affected subcommands:
- `nvm install` (no version + no .nvmrc)
- `nvm use` (version unresolvable)
- `nvm run` (no version + no .nvmrc)
- `nvm which` (no version + no .nvmrc)
- `nvm cache` (unknown subcommand)
- `nvm uninstall` (wrong arg count)
- `nvm unalias` (wrong arg count)
- `nvm install-latest-npm` (wrong arg count)
- `nvm reinstall-packages` / `nvm copy-packages` (wrong arg count)
The catch-all unknown-subcommand handler still dumps full help, since
in that case the user has no narrower context to be reminded about.
Refs #3755
