maintenance: Separate Code into Separate Files

This change breaks the monolithic src/libtorch.cc into multiple files,
with a modern separation of classes into separate header and code files.

Author: whoisj

CMakeLists.txt

@@ -280,6 +280,9 @@ add_library(
   src/libtorch.cc
   src/libtorch_utils.cc
   src/libtorch_utils.h
+  src/model_instance_state.cc
+  src/model_state.cc
+  src/string_utilities.cc
 )
 
 add_library(