Support / require pyramid >= 2.0

[tseaver]

~~Builds atop changes in #307. I will rebase this PR once that one merges.~~ Rebased after merge of #307.

Coverage is at 100%, and all tests pass for py38 through py312, except the ones for substanced.scaffold, which I just turned off. To appease our new insect overlords, we would likely need to make the scaffold into a cookiecutter template project.

I'm disabling a bunch of deprecation warning spew, mostly from chameleon (it interacts with Python AST internals in ways that will break under Python 3.14) and hypatia (maybe similar? I haven't checked).