[BUG] --save-dev and --save-optional are not mutually exclusive

[Sainan]

Is there an existing issue for this?

• I have searched the existing issues

This issue exists in the latest npm version

• I am using the latest npm

Current Behavior

Doing npm i --save-dev --save-optional <package> saves the package to optionalDepencies

Expected Behavior

I'd expect some sort of warning or error that the flags are mutually exclusive, or that the format of the flag is indeed --save=main, --save=dev, --save=optional because it seems to be more of an enum than booleans. See also #8188.

Steps To Reproduce

See above.

Environment

• npm: v10.9.2
• Node.js: v22.14.0
• OS Name: Windows 10