BASIS v1.15 causes `class-memaccess` warnings

[oznogon]

ubuntu-latest CI flags a warning for basisu/BASIS Universal:

/home/runner/work/SeriousProton/build/_deps/basis-src/encoder/../transcoder/basisu_containers.h:323:19: warning: ‘void* memcpy(void*, const void*, size_t)’ writing to an object of type ‘class basisu::vec<4, float>’ with no trivial copy-assignment; use copy-assignment or copy-initialization instead [-Wclass-memaccess]
  323 |             memcpy(m_p, other.m_p, other.m_size * sizeof(T));
      |             ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This doesn't impede other builds.

Our usage appears to be based on v1.15-update2. BASIS v1.16.3 changes this behavior (BinomialLLC/basis_universal@7a2094b), but I don't know if that resolves this warning.

v1.16.3 causes several breaking changes: mosra/magnum-plugins#119

[oznogon]

SP mocks up a library out of basis 1.15. The basis project moved the encoder and transcoder into a library with 1.50 (2024). 2.0 (2026) added pure C APIs.