Adding `test_pass_released_shared_ptr_as_unique_ptr`, exercising new guard in smart_holder_type_casters.h.

Now also passes the open_spiel iterated_prisoners_dilemma_test ASAN clean, in addition to all pybind11 and PyCLIF unit tests.

The problem was that calling `std::shared_ptr<void>::reset()` with a `void` pointer cannot possibly update the `shared_from_this` `weak_ptr`.

The solution is to store a `shd_ptr_reset` function pointer in `guarded_deleter` (similar in idea to the stored function pointer for calling `delete`).

This commit still includes all debugging code, i.e. is "dirty". The code will be cleaned up after the GitHub CI is fully successful.

First attempt to make shared_from_this and trampolines play nicely. Passes all pybind11 and PyCLIF unit tests ASAN clean, but not the open_spiel iterated_prisoners_dilemma_test.

Base version: https://github.com/rwgk/stuff/blob/e5318faa6a8583b7c338e01398a4eea69abda08d/shared_from_this_custom_deleters.cpp

This reverts commit febf9ce949c0bc87a8bf7ab3ddae4deb28636c9d.

This reverts commit d72d54ebb0b7784f5616edc02910dbd9cce0b2a4.

This reverts commit 59bc2e183e7aef5e45c06aed6965de0ac52d7b06.

This reverts commit 19c5a3613fee71878ba2af0339eed325a5916089.

Fully emulating type_caster_base-related behavior: trying shared_from_this also for unowned pointees.

enable_shared_from_this_from_raw_ptr_take_ownership_guard: better static_assert that also triggers for derived classes.

Restoring init_holder overload for std::enable_shared_from_this and original tests/test_smart_ptr.py.

Breaking up test_shared_ptr_from_this_and_references into smaller subtests. Skipping the only test that generates an ASAN heap-use-after-free.