Put a checksum into the `KmcountsCached` cache filename so different cases get independent cache files, e.g. when switching git branches, Parca options during parameter optimization, or mono/polycistronic operons.

This renames the cache file from `fixtures/endo_km/km3.cPickle` to `parca-km-1918837868.cPickle`, for instance.

Q. Does anyone prefer the "fixtures" directory name?

The cache files `cache/parca-km-*.cPickle` will accumulate until `make clean`.

Does this succeed in distinguishing current cases?

We could make this more sensitive by checksumming more inputs or less picky by rounding `Kmcounts.astype(np.float16)`.

See #1123

This `make clean` will clear the current Aesara cache if it's larger than a threshold. 30MB seems fair the cache is 11MB locally and 350 MB in `~tahorst` on Sherlock.

Aesara's cache management is not straightforward, partly to handle multiple processes and NFS.

1/2 of code review feedback: add isEndoRnase and alpha to the cache checksum calculation to account for all the loss function's inputs.

This should fix #996 by putting more cross-checks in the Km counts cache, but I don't have a test case for that.

Ideally we'd factor out this part of the very long `setKmCooperativeEndoRNonLinearRNAdecay()` function and add test cases for it.

Q. Should `arrays_differ()` set the absolute and/or relative tolerances?

Adding to the cache file grew it from 37K to 110K. That should be fine but

... which affects the cache file content so it's esp. good to fix before merging into master.