Per mod/docs/optimize-layer-design.md Stage 3 (continued). The mixins/optimize/
folder hit the project's ≤4 .java-files-per-folder rule when we tried to add
the next batch of mixin'ов (LivingEntityLodMixin, BubbleColumnUpParticleMixin,
LevelRendererOutlineMixin). Move the existing 4 mixin'ов into semantic subfolders:
- mixins/optimize/gl/GlCommandEncoderClearMixin.java (was mixins/optimize/)
- mixins/optimize/gl/GlCommandEncoderTexBufferMixin.java
- mixins/optimize/gl/RenderTypesMixin.java
- mixins/optimize/hud/OptimizeDebugHudMixin.java
lovisual.mixins.json: the 'client' array entries are updated to use the
new dotted paths (optimize.gl.*, optimize.hud.*). The package field in
each mixin file is updated to match.
No functional changes — this is purely a code-organization commit to make
room for the new Stage 3 mixin'ов in the next commit.