Csse pyd2 510 Part 2

[loriab]

Description

• currently atop Csse pyd2 510 #347

• pick over remaining relevant parts of @Lnaden Pydantic v2 Overhaul [DNM yet] #321 (below), then patch 'em up. so first commit is from Pydantic v2 Overhaul [DNM yet] #321 (note not a literal cherry-pick like Csse pyd2 510 #347) and second commit a1f7dcc are the fixes to get it working.
• Fix up DFTFunctional, CPUInfo to be pydantic v2 API only. (afaik, this was an effort that didn't go anywhere. they're not used in qcng. Anyone know of usage in the wild downstream?)
• Fix up Datum to be pydantic v2 API only. This is well-used, esp for NIST physical constant, but afaik it's never within a QCSchema model, so safe to support only one version.
• Fix up serialization of models. Tentatively, trying an in-class try/except/try/except to handle serializing both pyd v1 and v2 API models. It works for tests, but we'll see about real life.

Changelog description

Status

• Code base linted
• Ready to go
• DON'T SQUASH

[codecov]

Codecov Report

Attention: Patch coverage is 61.95652% with 35 lines in your changes missing coverage. Please review.

Project coverage is 87.27%. Comparing base (8f2d8b5) to head (a1f7dcc).
Report is 5 commits behind head on next2024.

Additional details and impacted files

[loriab]

Requesting review @davidbrownell, @krachwal, @rfievet, @ketanbj, @varun646, @jyoung3131