Refactor: move EXX file-list broadcast out of source_cell (#7635)

[Critsium-xy]

Background

Fixes #7635.

source_cell is a data-structure layer that should not depend on a higher layer. bcast_cell.cpp violated this by reaching into GlobalC::exx_info (owned by source_hamilt/module_xc) to broadcast the ABFS/JLE orbital-file lists:

#include "source_hamilt/module_xc/exx_info.h" // use GlobalC::exx_info
...
bcast_string_vector(GlobalC::exx_info.info_ri.files_abfs);
bcast_string_vector(GlobalC::exx_info.info_opt_abfs.files_abfs);
bcast_string_vector(GlobalC::exx_info.info_opt_abfs.files_jles);

Data lifecycle

These lists live in GlobalC::exx_info and flow:

1. Populate (rank 0): source_cell/read_atom_species.cpp parses ABFS_ORBITAL / ABFS_JLES_ORBITAL from STRU during setup_cell.
2. Broadcast (all ranks): previously in bcast_cell.cpp — the coupling this PR removes.
3. Consume: the LCAO EXX/RI code — Exx_LRI (RI-EXX), Exx_Opt_Orb::generate_matrix (opt-ABFs), RPA_LRI::postSCF (RPA).

Change

The ABFS/JLE orbital files are an LCAO-only concept, so the broadcast belongs with the LCAO EXX manager, not in source_cell or the generic XC module:

• Add bcast_exx_file_lists() in source_lcao/setup_exx.{h,cpp}.
• Invoke it at the start of Exx_NAO::init(), before Exx_LRI copies info_ri.
• Remove the exx_info.h include, the bcast_string_vector helper, and the three broadcast calls from bcast_cell.cpp.

Exx_NAO::init() is called from ESolver_KS_LCAO::before_all_runners — reused by TDDFT / DM2rho / DoubleXC (they call the base), while LR reuses the already-built Exx_LRI via move_exx_lri. It runs on all ranks, after setup_cell populated the lists on rank 0 (driver calls setup_cell before before_all_runners), and before every consumer:

• RI-EXX: the Exx_LRI copy of info_ri happens right after the broadcast inside init().
• opt-ABFs: generate_matrix runs later in the same before_all_runners.
• RPA: RPA_LRI(GlobalC::exx_info.info_ri) is built in ctrl_scf_lcao during the SCF run, after before_all_runners.

After this, bcast_cell.cpp no longer depends on any higher layer.

Behaviour

Preserved. The broadcast still runs after the rank-0 populate and before any EXX consumption. The previous per-ionic-step re-broadcast (via bcast_unitcell in update_cell.cpp during relax/MD) is dropped, which is behaviour-neutral because the file lists are static once read from STRU.

Because __EXX implies __LCAO (LibRI requires ENABLE_LCAO), setup_exx.cpp is always built whenever the broadcast is compiled.

Verification

• Repo-wide grep confirms bcast_cell.cpp has no remaining exx/GlobalC reference; the only remaining exx_info user in source_cell is read_atom_species.cpp (write side — see note).
• g++ -std=c++14 -fsyntax-only passes on the broadcast function body compiled against the real exx_info structs (MPI headers stubbed locally). setup_exx.cpp itself pulls LibRI/cereal and so is exercised by CI rather than locally.

Note (out of scope)

The write side — source_cell/read_atom_species.cpp parsing the ABFS STRU sections into GlobalC::exx_info — still couples source_cell to the XC layer. #7635 is specifically about the broadcast in bcast_cell.cpp; moving the ABFS STRU-section parsing out of source_cell is larger and best handled as a follow-up.

Global dependency budget (governance)

This PR is migration-neutral for the GlobalV::/GlobalC::/PARAM budget: the three GlobalC::exx_info broadcast calls are moved from bcast_cell.cpp to setup_exx.cpp (-3/+3, net zero in code), and source_cell is fully decoupled from the XC layer. No new global-state coupling is introduced.