single precision support in skimage.segmentation

[grlee77]

Description

This PR adds float32 support to most functions in skimage.segmentation.

random_walker and slic already had float32 support, but some additional tests were added.

I skipped felzenswalb and watershed for now as the Cython code for these was a little more involved, so those two still promote to double precision internally.

Checklist

• Docstrings for all functions
• Gallery example in ./doc/examples (new features only)
• Benchmark in ./benchmarks, if your changes aren't covered by an
  existing benchmark
• Unit tests
• Clean style in the spirit of PEP8

For reviewers

• Check that the PR title is short, concise, and will make sense 1 year
  later.
• Check that new functions are imported in corresponding __init__.py.
• Check that new features, API changes, and deprecations are mentioned in
  doc/release/release_dev.rst.

[pep8speaks]

Hello @grlee77! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2021-05-04 01:00:08 UTC

[rfezzani]

Excellent @grlee77, I just left a code formatting suggestion 😉. Thank you!

[mkcor]

Thank you for all the cleanup as well!