feat(rpa): modularize RPA and extend LibRPA exports

[AroundPeking]

Summary

This PR consolidates the RPA-related work into dedicated modules while preserving the existing EXX workflow.

RPA and Delta-Sternheimer

• Separate RPA, LibRPA I/O, and Delta-Sternheimer implementation paths from the EXX code path.
• Add a modular module_rpa layout with dedicated Delta-Sternheimer and LibRPA I/O components.
• Add molecular and periodic Delta-Sternheimer response generation, including response-grid, finite-difference, auxiliary-basis, channel-parallel, and MPI handling.
• Write periodic Delta-Sternheimer response files consistently below the configured RPA output directory.
• Add auxiliary-basis preorthogonalization and conditioning support for RPA response construction.
• Keep GreenX/minimax integration optional through an external dependency interface rather than vendoring the dependency into ABACUS.

LibRPA Interface

• Extend reader-v1 export of Coulomb, response, LRI, auxiliary-basis shrink, band, exchange-correlation potential, and LCAO wavefunction data.
• Use the current output naming and directory layout expected by the updated LibRPA reader.
• Add MPI-safe output for KS eigenvectors and related LCAO producer data.
• Export spatial and spin-symmetry metadata through stru_out; LibRPA reconstructs symmetry operations from this file without legacy symrot_* sidecars.
• Support nonmagnetic, collinear spin-polarized, SOC, and SOC magnetic-symmetry producer paths.

2D and Symmetry Support

• Add strict-2D Coulomb and analytic head/wing export support for RPA and GW workflows.
• Extend symmetry-aware RPA/GW producer output, including shrink and spin-resolved data paths.
• Preserve the existing EXX behavior while making RPA-specific functionality independently maintainable.

Regression Coverage

• Add independent ABACUS producer checks for ordinary RPA, 2D RPA/GW, SOC, SOC magnetic symmetry, nspin = 2, and Delta-Sternheimer.
• Check stable LibRPA-consumed artifacts including stru_out, Coulomb, response, LRI, shrink, band, and potential outputs.
• Keep the existing BSE and other regression cases unchanged.