Scipy integration and other fixes

[weaverba137]

This PR supersedes PRs #90, #87, #86.

In particular:

• Both #90 and #87 had proposed fixes to new function names in scipy.integrate. This PR handles that fix at the import level.
• The deprecation of pkg_resources as suggested in #86 is incorporated, although currently speclite is tested against Python versions that do not have importlib.resources.files, so it is still necessary to support both so that tests pass.
• matplotlib >= 3.3 requires Pillow. Pillow 10.4 requires numpy >= 1.21, but many of the tests require numpy <1.21. Pinning to Pillow<10.4 gets all the tests working again.

[weaverba137]

Thank you @dkirkby. I'm merging now to prepare for the next round of fixes.