collapse register mode into being a thread space, unify process/thread/debugger read/write paths, keep differences in core eval read/write paths

src/eval/eval_parse.h

@@ -139,6 +139,7 @@ struct E_ParseCtx
   // rjf: instruction pointer info
   U64 ip_vaddr;
   U64 ip_voff;
+  E_Space ip_thread_space;
   
   // rjf: modules
   E_Module *modules;