Fix ThermoML parsing

[lilyminium]

Actually relates to this dimsim issue (openforcefield/dimsim#53) but it's a shared issue as the ThermoML code was simply ported.

Edit: I messed up and rebased this off of #754 by accident, sorry

[codecov]

Codecov Report

❌ Patch coverage is 80.48780% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.28%. Comparing base (8406372) to head (f0b293d).
⚠️ Report is 2 commits behind head on main.

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[lilyminium]

Well, the test errors here actually suggest I should have been blaming OpenEye, not RDKit, oops.

Edit: I take it back -- I put in the oechem skip condition for the fix and then immediately forgot about it. It's RDKit!

[mattwthompson]

This looks good but I found two one thing] I would like another look at; neither call for re-review if the outcomes are as expected

1. A blocking comment in the code about behavior when RDKit is not installed which can be resolved by you agreeing it's an okay and intentional change. No need to re-review just for that
2. Triggering the failing test (#757), i.e. that check failing as expected -- now resolved: test failing/skipped as expected: https://github.com/openforcefield/openff-evaluator/actions/runs/23498429535/job/68386169870?pr=757

[mattwthompson]

This block isn't hit by code coverage, which from my reading of the test is because the new, correct behavior requires OpenEye. I think this is okay in the current context of all relevant stakeholders having access to a license, but we should document that this case is bad without an OpenEye license

[lilyminium]

It now raises a warning if openeye isn't available.

[mattwthompson]

(non-blocking, see comment in an except block below) it would be nice if this test encoded that the old/bad behavior persists without this license, not necessarily saying that is a desirable outcome but the test should capture the behavior we think happens

[lilyminium]

I split out this test to test the case where openeye both is and isn't installed.