analysis: lock mixin classes and plugin again (revert mixin rename)

Renaming mixin classes and patching mixins.json (90506a4) breaks Fabric
mods at runtime, proven on LoVisual (2026-10-13):

- When obfuscated packages are randomized per class the config patcher
  computes an empty common prefix and writes `package: ""`. Fabric/Mixin
  then drops every mixin as "orphaned", so `RenderPipelineMixin
  implements IRenderPipeline` never applies, the interface is not
  injected into `RenderPipeline`, and the entrypoint dies with
  `ClassCastException: RenderPipeline cannot be cast to IRenderPipeline`.
- `IMixinConfigPlugin.shouldApplyMixin` compares the runtime mixin class
  name against string literals (`Set.of("dev.loki...Mixin")`); renaming
  desyncs those sets and optional sodium/iris/xaero mixins get applied
  when the target mod is absent.

Re-enable absorb_mixins: mixin entry classes and the config plugin keep
their names, and locking a class freezes its members too (needed for
@Accessor/@Invoker/@Overwrite name lookups). Calls from locked mixin
bytecode are still rewritten consistently, and the family mechanism keeps
interface method names (IRenderPipeline) in sync with the frozen mixin
methods. patch_mixins_json stays but is identity for locked classes.

Verified: LoVisual obf jar loads all 221 mixins (0 orphaned), the main
menu renders, the entrypoint runs.

crates/noxis-analysis/src/keep/mod.rs

@@ -168,6 +168,7 @@ impl Analysis {
         keep.absorb(&entrypoints);
         keep.absorb_bootstrap(program);
         keep.absorb_databind(program);
+        keep.absorb_mixins(program);
 
         let locked_classes = program
             .classes