[master] Wrong caching of overrides (#3465)

* override: Fix wrong caching of the overrides

There was a problem when the python type, which was stored in override
cache for C++ functions, was destroyed and  the record wasn't removed from the
override cache. Therefor, dangling pointer was stored there. Then when the
memory was reused and new type was allocated at the given address and the
method with the same name (as previously stored in the cache) was actually
overridden in python, it would wrongly find it in the override cache for C++
functions and therefor override from python wouldn't be called.
The fix is to erase the type from the override cache when the type is destroyed.

* test: Pass by const ref instead of by value (clang-tidy)

* test: Rename classes and move to different files

Rename the classes and files so they're no too generic. Also, better place to
test the stuff is in test_virtual_functions.cpp/.py as we're basically testing
the virtual functions/trampolines.

* Add TODO for erasure code

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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