[DRAFT] Non-Boolean conditional pass

[tob-joe]

This includes:

• An updated constant-propagation implementation that adds support for tracking uncertainty about the exact value (e.g. Boolean(None), which is definitely boolean but doesn't have a known exact value)
• A new analysis that finds conditionals that expect boolean values but are being passed not-definitely-boolean values
• The flake.nix that pulls in rust 1.65.0 for development

Things are a little sloppy and I have not tested the new features properly so I'm leaving it as a draft for now.

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:white_check_mark: fegge
:x: tob-joe
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