the `org.eolang.maven.optimization` package is over-design

[yegor256]

I believe that the org.eolang.maven.optimization package is not necessary -- all classes from it may be placed right into the OptimizeMojo, in order to improve readability.

[ArtemGet]

@yegor256 In addition, i wish to add some more improvements and tests, but it would be too much for 1PR.
I.E replacing the OptTrain.DEFAULT_TRAIN constant or replacing optimization() methods in Mojo's to something like:

new OptSpyFork(
  ()-> //reason to spy
  ()-> new OptimizeMojo.OptSpy(...),
  ()-> new OptimizeMojo.OptTrain(...)
)

WDYT?

[yegor256]

@ArtemGet I'd suggest to start with the smallest PR possible, it will help us review it faster