Refactor source_psi, remove some unnecessary dependency

[mohanchen]

Refactor source_psi, remove some unnecessary dependency

[Critsium-xy]

There are some not small problems🫠

[Critsium-xy]

Second comment: a design suggestion on the new prepare_params() / initialize() split. Not a correctness problem, but since it is an interface shape this PR newly introduces, it is much cheaper to settle now than after callers accumulate.

(This is dyzheng play😋)

[Critsium-xy]

Three minor cleanup points, none blocking.

[Critsium-xy]

Naming: psi_base is a weaker name than psi_initializer, and it collides conceptually with psi::Psi.

psi_initializer named the responsibility; psi_base names a position in the class hierarchy. The responsibility has not changed -- the comment right above this line still says "This class is used to allocate memory and give initial guess for psi", and the usage sequence documented there is still new->initialize->tabulate->init_psig. So the new name carries strictly less information than the old one.

The more concrete problem is that the file now sits next to source_psi/psi.h as source_psi/psi_base.h, which reads as "base class of psi::Psi". No such relationship exists, and a reader has to open the file to find that out.

If the goal is just to shorten the psi_initializer_* prefix -- and psi_init_atomic etc. are a genuine improvement -- then psi_init_base (or psi_init) keeps that gain while still describing the role, and matches the new CMake target name psi_init introduced in this PR. Worth settling before the name spreads: it is a sed today, and a much wider diff once other modules start referring to it.