$_
nvm.sh
nvm.sh uses `NVM_SCRIPT_SOURCE="$_"` to detect its source location. Adding `: nvm.sh` before each source line ensures `$_` is set correctly, preventing breakage when the previous command (e.g., `set -ex`) overwrites it.
863bd63
Leaves 2 non-executable, + some TODOs
nvm_install_binary_extract