Status Tracking: `chemprop` and ML Thermochemistry Prediction

[JacksonBurns]

Summary:

• RMG currently uses chemprop version 0.0.1 to perform machine learning prediction of molecular thermochemistry
• This version only supports Python version 3.7 and 3.8, so it is blocking the upgrade of RMG to Python 3.11/12
• chemprop will be temporarily removed from RMG to allow upgrading Python versions

This was the original PR where removing chemprop was started, and was eventually folded into #2553.

The eventual re-integration of chemprop will be dependent on the first stable release of v2 (and other steps mentioned in the first linked PR) detailed in this issue:

• [x] https://github.com/chemprop/chemprop/issues/517

[JacksonBurns]

@KnathanM has agreed to start some basic feasability checks for the re-addition of Chemprop for thermochemistry prediction