feat(policy network stack): Policies can now return the network stack

Policies can now return the network stack which allows the caller more
control over settings and running a solver against various levels of the
stack. Further, policies can return the partition function used as well
as a vector of enums which describe the structure of the network stack.

src/meson.build

@@ -9,6 +9,7 @@ gridfire_sources = files(
     'lib/engine/procedures/priming.cpp',
     'lib/engine/procedures/construction.cpp',
     'lib/engine/diagnostics/dynamic_engine_diagnostics.cpp',
+    'lib/engine/types/jacobian.cpp',
     'lib/reaction/reaction.cpp',
     'lib/reaction/reaclib.cpp',
     'lib/reaction/weak/weak.cpp',