Update version detection

[dopplershift]

Description Of Changes

Try to avoid pulling in setuptools_scm for better import time by directly checking for a pip file that indicates whether the install is editable and only using the git-based version in that case; otherwise, depend on the distribution metadata.

Alternative to #3363.

[dopplershift]

@akrherz Does this accomplish the same optimization you saw in #3363?

[akrherz]

Wow @dopplershift, there's python foo I have never seen before here, ufff. Indeed, testing this

import metpy

check	main	this PR
timing	1.4s	1.1s
memory (memray)	92.2 MB	88MB

[dopplershift]

Regarding tests and coverage, I believe our thinking in the past was that we make sure CI covers the path for the released code, and our dev installs will cover...well the dev path. I don't think there's a good way to test this that doesn't essentially mock things out based on the implementation or require another CI job that uses a dev-style (editable) install.

[dopplershift]

@dcamron We can ignore the coverage failure here, so this is ready for review.

[dcamron]

Sounds good. I'd meant to make room for the testing/coverage discussion, but I'm happy with your summary above. 👍

[dopplershift]

The important part is that we don't release a broken package, and I'm confident we're testing for that.