Fix issue #447

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This PR closes #447 by increasing the maximum mass used to detect hydrogen atoms along with exposing a map option to tune the value.

@chryswoods: In case I'm missing something: Is there a reason why 2.5 was chosen? This does work with what would be used for the default SOMD1/SOMD2 HMR factor, but not in general.

Also closes #449 by considering both end states when adding initial entries to the ghost-14 force.

Also closes #450 by constraining unperturbed heavy atom bonds, regardless of mass, matching SOMD1.

• I confirm that I have merged the latest version of devel into this branch before issuing this pull request (e.g. by running git pull origin devel): [y]
• I confirm that I have added a changelog entry to the changelog (we will add a link to this PR as part of the review): [y]
• I confirm that I have permission to release this code under the GPL3 license: [y]

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I bumped the threshold to 4.5 and set a max h_mass_factor in SOMD2 of 4.0. This would also catch He, but that shouldn't be an issue for biomolecular simulations.

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Actually, having thought more about this, a value of around 3.5 is safest. I've also updated the BioSimSpace and SOMD2 code to place an upper bound so that we don't end up with negative masses for heavy atoms.

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I've also added a warning for situations where the HMR factor produces a negative heavy atom mass.

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The tests appear to be failing due to a kartograph API change. I'll figure out what's changed and update. It might be that we need to add a pin.

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Despite the CI passing yesterday we are now seeing a repeated test failure for Linux Python 3.11 for a completely unrelated test (AMBER CMAP parsing). This is reproducible across CI runs. Will investigate on Monday.