Python 3.7-3.8 and Pydantic v2

[dan-fritchman]

Originally noted in: https://github.com/dan-fritchman/Hdl21/issues/157#issuecomment-2023271671

Python 3.7 and 3.8 continue to work, if you use Pydantic v1. E.g.: https://github.com/dan-fritchman/Hdl21/actions/runs/8455642769

If there's some dependency specification mechanism to state that, great.
If not we may just be Python 3.9+ from here on.

[dan-fritchman]

Further noting:

• Hdl12 uses dataclass absolutely everywhere. So there is no chance of ever supporting Python before 3.7.
• If there are any users who need (or just want) 3.7 or 3.8 support, this is your place to speak up. Not quite "speak now or forever hold your piece", but getting there.

[dan-fritchman]

Courtesy @daquintero:

Ahh this is great for the next release, thanks! The diagram is from here https://devguide.python.org/versions/ and it's really helps managing the target support for releases imo

That is quite helpful to know.

I am nonetheless quite reticent to leave Python versions behind. This is a package for chip designers, a bunch who is absolutely horrendous at upgrading any piece of software ever. Case in point: many such orgs have just managed to upgrade to their "new" OS of choice - RedHat Linux v7, just in time for it to go EOL next month. Maybe python itself has gotten easier in this sense, since the meta-managers (e.g. conda) have made it easier for each user to install their own version. But I expect plenty of noobs (our audience) will be pegged to what their CAD group allows, and that will perennially be old as dirt.

So, if we can keep Python 3.7-3.8 working we should.
Again given Hdl21's design (particularly the pervasive dataclasses), there's no hope of supporting any earlier than 3.7. So it's really those two sub-versions in question.