Porting fast FESOM/RECOM to main branch

[JanStreffing]

During the AWI-CM3/AWI-ESM meeting we talked about the RECOM code sped up by Kai Himstedt and currently in use by @a270105. My idea would be to investigate whether these FESOM2 trace code speed ups / better parallelization would work in the refactoring branch. If they do, let talk about whether we want to add them there before the next FESOM2 release or after.

@mbutzin @mwerner-awi @chrisdane

[JanStreffing]

Could you point out on which branch these changes reside and which commits they comprise?

[a270105]

Hi Jan, you can find the code that I am using in the branch fesom-2.1-recom-paleo. There is also a new merged version of my branch and Ozgur's fesom2.1_recom branch. This new one can be found in the branch fesom2.1_recom3_merge. But it is still being tested now.

[JanStreffing]

Will be closed through merger of #681