Rework installer and requirement checks

[akx]

This PR:

• moves requirements from requirements.txt to the standard TOML project.dependencies list
• guts install.py to move everything version-specific to sd_dynamic_prompts.version_tools
  • We now just always attempt to install the requirements from requirements. No good reason not to, IMO :)
• switches to using packaging's utilities to check whether the currently installed dynamicprompts version matches our specifier; this means e.g. future [compatible] versions of dynamicprompts work without having to bump the requirement here; e.g. ~=0.25.2 is fine with any 0.25 series >= 0.25.2, ~=0.25 is fine with any 0.x >= 0.25, etc. This also allows using actual ranges, if we need to, in the requirements, e.g. ~=0.25.2,<0.30 (but hopefully it never gets to that).
• improves the messaging a bit (though the formatting maybe got worse c.f. An incompatible library version disables the extension. #447); see screenshot.

Screenshot

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Follows up on #447, #450
Fixes #437

[adieyal]

Shoot - didn't realise that you were working on this now. I just pushed some temporary changes in anticipation of your update. Feel free to revert my PR.

[akx]

@adieyal No worries, rebased :)

[adieyal]

I'm getting a ModuleNotFoundError:
ModuleNotFoundError: No module named 'tomli'

[akx]

@adieyal ah, good catch...

[akx]

@adieyal I pushed a new commit that adds compatibility imports for TOML and Packaging from pip's vendored libraries and tried that this works fine on e.g. a python:3.9 Docker image. I think we should be safe to assume that our users don't use a three-year-old pip, and if they do, they should upgrade.

This is conflicting on 53e69fe though (#479).