sound_source and the gl::object conversion operators stay implicit; they
are relied upon by copy-list-initialisation and GL calls.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
TSegment::GetTFromS() is a significant hotspot in the non-rendering part of the state_manager update (about 13%). This change introduces a FastGetTFromS() version that interpolates from precomputed values instead of doing the whole calculation on every call. Computing position from track distance is now done in constant time. This reduces the contribution to about 0.3%.
