perf: Add object rvalue overload for accessors. Enables reference stealing (#3970)

* Add object rvalue overload for accessors. Enables reference stealing

* Fix comments

* Fix more comment typos

* Fix bug

* reorder declarations for clarity

* fix another perf bug

* should be static

* future proof operator overloads

* Fix perfect forwarding

* Add a couple of tests

* Remove errant include

* Improve test documentation

* Add dict test

* add object attr tests

* Optimize STL map caster and cleanup enum

* Reorder to match declarations

* adjust increfs

* Remove comment

* revert value change

* add missing move