Refactor Slice 3B: Move build logic into `CIME/core/build/`

[jasonb5]

Part of #4950. Slice 3B of 5. Estimated 5 weeks. Depends on #4998.

Goal

Move build logic from build.py (1350 lines) into focused modules under
CIME/core/build/. Keep CIME/build_scripts/ as the stable external wrapper.

Tasks

Extract into CIME/core/build/

• Build planning logic.
• Build execution / orchestration.
• build.py becomes a thin re-export layer.

Move from utils.py

• analyze_build_log, run_bld_cmd_ensure_logging,
  copy_local_macros_to_dir → core/build/.
• safe_copy, safe_recursive_copy, symlink_force, copy_globs,
  copy_over_file, copyifnewer → CIME/core/fileops.py (build is heavy
  consumer, pulled here).

Consolidation — free functions taking case

• case_build(), clean(), _clean_impl(), post_build() (build.py)
  currently access case._gitinterface (private!), call case.get_value,
  case.set_value, case.flush(). Make them Case methods that delegate
  to core/build/.
• get_standard_cmake_args(), get_standard_makefile_args(),
  uses_kokkos() (build.py) extract ~15 values from Case.
  Consolidate as Case methods or a BuildConfig data class.
• generate_makefile_macro() (build.py) calls case.get_value() —
  same pattern.

Deduplicate copy functions

• Four overlapping copy functions in utils.py (safe_copy,
  copy_over_file, copyifnewer, copy_globs) → coherent
  CIME/core/fileops.py API.

Sharedlibs (resolves #4837)

• Sharedlibs list currently hard-coded; expose as configurable.

Imports & re-exports

• Update internal CIME imports to core/build/.
• Keep re-exports in build.py and utils.py.
• CIME/build_scripts/ unchanged — stable external interface.

Definition of done

• All build tests pass.
• CIME/build_scripts/ compatibility maintained.
• External models (E3SM, CESM, NorESM) build unchanged.
• No private-attribute access (case._gitinterface etc.) from outside Case.
• One coherent fileops API; no four-copy-function-zoo.
• Resolves The set of sharedlibs needed by a model should not be hardcoded #4837.

Related

• Resolves The set of sharedlibs needed by a model should not be hardcoded #4837 (sharedlibs hard-coding)
• Depends on Refactor Slice 3A: SRCROOT standardization (remove config_files.xml) #4998 (config loading must be stable first)
• Blocks Refactor Slice 4: Decompose Case god object #5000 (Case build delegation comes from this slice)