Clear internal caches when re-creating from same SMIRNOFF objects

[mattwthompson]

Description

Another possible fix for #1453, including the test @j-wags added

A problem with the _clear_cache function introduced in #1435 is that it went through all objects visible to the garbage collector (!) and only interacted with objects that are themselves internal to the openff.interchange namespace. This is casting a net that is awfully wide and unnecessary since we already know what caches we want to clear. Since the crux of the bad behavior can be traced to two internal functions (see here for a good example) we don't need to iterate so widely.

Put another way: the problematic cached functions¹ are only two in number and inside of Interchange. We can just clear those specific function caches directly when we need to.

Checklist

• Add tests
• Lint
• Update docstrings

Footnotes

1. and they do nothing but look up parameters inside of ParameterHandlers, see https://github.com/openforcefield/openff-toolkit/issues/2065 ↩

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.06%. Comparing base (14cd931) to head (d981804).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1456      +/-   ##
==========================================
- Coverage   94.07%   94.06%   -0.02%     
==========================================
  Files          73       73              
  Lines        6045     6034      -11     
==========================================
- Hits         5687     5676      -11     
  Misses        358      358              

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