Avoid adjusting input entries in mixing schemes.

[peikai]

Here to submit changes to avoid change input entries in place.

In both of GGA/GGA+U and GGA/GGA+U/R2SCAN mixing processes, the methods below not only return adjusted entries, but also change input entries in place. Is it necessary? I think this may cause bugs in programming.

MaterialsProjectDFTMixingScheme.process_entries()
entries.compatibility.process_entries()

Thanks!

[coveralls]

Coverage: 74.3% (-5.2%) from 79.463% when pulling 7606c36 on peikai:EntriesCopy into c6f9bba on materialsproject:master.

[peikai]

The usage of process_entries() method needs attention. It only returns the entries that have been processed, not always the complete set of adjusted entries. If input entries have contained energy adjustments, they would not be processed again, and even would not be shown in the results that are returned (if process_entries(clean=False)).

In the case, processed_entryList = compatibility.process_entries(entryList, clean=True), entryList will be changed as well.
In the case, processed_entryList = compatibility.process_entries(entryList, clean=False), processed_entryList may not have a complete set of entries, if there are some entries containing energy_adjustements in entryList.

I would close this PR, to avoid changing this usage.

[peikai]

This PR is renewed in #2841.