fix: missing dependency on packaging

[henryiii]

This is used, but not declared. So many packages depend on this that it's being always pulled in for testing, but in a minimal environment it's missing.

See pyodide/pyodide#4767 (comment).

[HDembinski]

Oh, I was under the impression that is a stdlib package. In that case, I should replace it, but for the time being, this is the right fix.

[henryiii]

I wouldn’t recommend replacing it, it is by far the standard tool for this. But it’s not distributed as part of the standard library because it needs to update at a higher frequency.

[HDembinski]

I only use it to parse the version number. That can easily be replaced.

[henryiii]

It is the canonical way to parse version numbers, and is a more reliable dependency than numpy, so IMO it's completely fine as a dependency. It's a dependency of pip even.

[henryiii]

(Not saying you can't remove it if you really don't want it, just saying I think it's not a net positive to remove it. Same goes for other packages from the CPython core developers, like typing-extensions.)

[HDembinski]

It is said in the README that iminuit's only hard dependency is on numpy. That is in its simplicity beautiful and I tend to keep it that way. You make good points, but this is a matter of style.