Update InteractiveSceneEmbed (#2267)

* Comment tweak

* Directly print traceback

Since the shell.showtraceback is giving some issues

* Make InteracrtiveSceneEmbed into a class

This way it can keep track of it's internal shell; use of get_ipython has a finicky relationship with reloading.

* Move remaining checkpoint_paste logic into scene_embed.py

This involved making a few context managers for Scene: temp_record, temp_skip, temp_progress_bar, which seem useful in and of themselves.

* Change null key to be the empty string

manimlib/module_loader.py

@@ -146,7 +146,7 @@ class ModuleLoader:
         if ignore_manimlib_modules and module.__name__.startswith("manimlib"):
             return
         if module.__name__.startswith("manimlib.config"):
-            # We don't want to reload global config
+            # We don't want to reload global manim_config
             return
 
         if not hasattr(module, "__dict__"):