Only warn if forces mismatch in hash check

[IAlibay]

Fixes #1913

This unfortunately makes system checking much weaker. I don't think there's much of a way around though:

1. There's no way for us to know which two forces should match (i.e. we can't rely on names or force groups).
2. Small changes in floats will change the hash.

That being said, the exact System check is overly cautious. Generally, this mismatch would happen (where the particle numbers match and the number of forces match and the barostat matches) in cases where someone is actively trying to do something bad (i.e. the risk of it happening accidentally is low to non-existent).

Checklist

• All new code is appropriately documented (user-facing code must have complete docstrings).
• Added a news entry, or the changes are not user-facing.
• Ran pre-commit: you can run pre-commit locally or comment on this PR with pre-commit.ci autofix.

Manual Tests: these are slow so don't need to be run every commit, only before merging and when relevant changes are made (generally at reviewer-discretion).

• GPU integration tests
• example notebook testing
• packaging tests: run this for any large feature PRs or PRs that add test data.

Developers certificate of origin

• I certify that this contribution is covered by the MIT License here and the Developer Certificate of Origin at https://developercertificate.org/.

[IAlibay]

pre-commit.ci autofix

[codecov]

Codecov Report

❌ Patch coverage is 16.00000% with 42 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.51%. Comparing base (b501e2e) to head (d1a46d3).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...fe/tests/protocols/openmm_ahfe/test_ahfe_resume.py	16.00%	21 Missing ⚠️
...sts/protocols/openmm_rfe/test_hybrid_top_resume.py	18.18%	18 Missing ⚠️
...openfe/protocols/openmm_utils/system_validation.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1914      +/-   ##
==========================================
- Coverage   94.69%   90.51%   -4.19%     
==========================================
  Files         210      210              
  Lines       18808    18841      +33     
==========================================
- Hits        17811    17054     -757     
- Misses        997     1787     +790     

Flag	Coverage Δ
fast-tests	90.51% <16.00%> (?)
slow-tests	?

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[IAlibay]

pre-commit.ci autofix

[jthorton]

lgtm lets get this in now and look to improve the check later!

[github-actions]

No API break detected ✅