Feat(deltaspin): add DeltaSpin for PW basis (nspin=1/2/4), lambda update strategies, and direction_only mode

- Port DeltaSpin to PW basis for nspin=1/2/4
- Add lambda update strategies: BFGS, full/incremental, controlled by sc_lambda_strategy
- Add direction_only constraint mode for noncollinear calculations (sc_direction_only)
- Add sc_scf_thr_mode parameter (off/immediate)
- Add sc_strategy and sc_dir_phase1_steps parameters
- Fix E_lambda formula: -sum(lambda*(Mi-Mtarget)) instead of -sum(lambda*Mi)
- Unify lambda sign convention to E' = E + lambda*(M - Mtarget) across PW and LCAO
- Fix reduce_double_allpool communicator size (GlobalV::NPROC_IN_POOL)
- Fix run_lambda_loop iteration indexing in PW path
- Fix SCF crash and charge-density sync issues in LCAO DeltaSpin
- Fix segfault in cal_escon() by adding empty-check guard
- Fix memory leak in cal_pre_HR() when reinitialized
- Propagate current_spin through operator chain in init()
- Add nspin=1 support for PW DeltaSpin and fix collinear constraint
- Add #ifdef __LCAO guards for LCAO-only code
- Refactor: cache PARAM.inp values, add SpinConstrain getters
- Add comprehensive DeltaSpin documentation
- Add tests for sc_scf_thr_mode, sc_dir_phase1_steps, and direction_only
- Includes DFT+U PW basis fixes (issue deepmodeling#7726)

Author: dyzheng