extract manual optimization loop

[awaelchli]

What does this PR do?

Part of #7938
Follow up to #9191
Fixes #9283

Now that automatic optimization is separated into its own loop, we can finally drastically simplify the calls to manual optimization and move it to a separat loop class.

TODO:

• make mypy happy

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[carmocca]

Noticed this while resolving conflicts: this is not called anymore, is it? Is that intentional?

(personally lean towards removing the running loss, so this would be okay): see #9372

[awaelchli]

technically this should not have been removed, ... sigh
but yeah, we can see what happens with #9372