feat(C-API): C API now can use multi-zone solver

C api has been brought back up to support and can use paraellization along with multi zone solver

tests/extern/C/meson.build

@@ -1,5 +1,11 @@
-executable('test_c_extern', 'gridfire_evolve.c',
+executable('gf_extern_c_single', 'gridfire_evolve_single.c',
   install: false,
   c_args: ['-Wall', '-Wextra'],
   dependencies: [gridfire_extern_dep]
-)
+)
+
+executable('gf_extern_c_multi', 'gridfire_evolve_multi.c',
+           install: false,
+           c_args: ['-Wall', '-Wextra'],
+           dependencies: [gridfire_extern_dep]
+)