src: split s_hllc_riemann_solver into m_riemann_solver_hllc

NFC, pure motion; completes the m_riemann_solvers split. State access stays host-associated via m_riemann_state; hllc additionally uses m_bubbles (f_cpbw_KM), m_bubbles_EE (rs/vs/ps), and m_surface_tension (s_compute_capillary_source_flux). With the last solver body gone, core drops the use-lists whose final consumers moved (m_variables_conversion, m_bubbles, m_bubbles_EE, m_surface_tension, m_chemistry, m_thermochem, the m_constants only-list) and the inline_riemann include; core keeps the dispatcher, module init/finalize, and the public re-exports. Statement-multiset union vs the pre-split file differs only by module boilerplate; GPU-directive census md5 unchanged; declare-target scoping verified for all six files.

Author: sbryngelson

docs/module_categories.json

@@ -10,6 +10,7 @@
             "m_riemann_solver_hlld",
             "m_riemann_solver_hll",
             "m_riemann_solver_lf",
+            "m_riemann_solver_hllc",
             "m_muscl",
             "m_variables_conversion",
             "m_thinc"