The copy constructors for `animrig::Strip`, `animrig::Slot`, and
`animrig::StripKeyframeData` used a `memcpy` call as part of the copy
implementation. However, this produced warnings on clang 20. For example:
```
warning: first argument in call to 'memcpy' is a pointer to
non-trivially copyable type 'blender::animrig::Strip'
[-Wnontrivial-memcall]`
```
These warnings did not reflect any actual bugs, because the underlying DNA
structs that those types wrap are in fact trivial. Nevertheless, it's worth
fixing the warnings.
This fixes the warnings by replacing the uses of `memcpy` with equivalents that
amount to a `memcpy` anyway, but which the compiler understands are valid for
the types.
There was also one additional use of `memcpy` in `Strip::create()` that did not
trigger a warning because it operated directly on the underlying DNA struct, but
was also unnecessary. This PR also replaces that with a simple assignment.
Pull Request: https://projects.blender.org/blender/blender/pulls/137467
b69a4380b6