new casida solver (#194)

* A+B subspace

* new casidai solver, project A+B into a+b, better; TODO: add dynamic polarizability

* cleanup unused funcs

* fix ECD mdpol bug due to assume ERI symmetry

* more reliable auxmol in the case of ECP

* no such ECP bug

* style fix

* style fix

* line style fix

* comments cleanup

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Co-authored-by: jojo <zhouzehaosuda@gmail.com>

Author: John-zzh