Adds src/jolt/aot.janet: save-ns / load-ns-image marshal a namespace's compiled
var cells to a Janet bytecode image and load them back, skipping
parse/analyze/emit/compile on reload.
Compiled functions close over core fns (cfunctions) that can't marshal by value,
so we marshal against a dictionary built from the baked-in runtime env
(env-lookup jolt-runtime-env, which chains to the Janet boot env): core fns and
builtins are referenced by name, only user bytecode and its var cells are
serialized. The runtime env is identical at save and load time (same binary), so
the dictionaries match.
Test round-trips a namespace (constant, fn over it, core-fn user, recursion) into
a fresh context and confirms the loaded vars run and stay redefinable.
