fix: ensure coalesce handles optional/unknown/null properly

[sgulseth]

We weren't really handling coalesce well:

1. We were pushing null into the list of possible types
2. We weren't handling unknowns
3. Even if we encountered a node that could never be null due to non-optional or no nulls in union we were still continuing

Opted to remove the snapshot and rather be explicit

[judofyr]

Tests look good and then I'm happy 🥳 Haven't looked deeply into the logic itself, but if we think there's still some bugs there I think we should rather invest in getting the typeEvaluateCompare tests on coalesce since we can then test a lot of combinations.

[sgulseth]

yess, agree on the compare 🙃 Soon!