remove dead code: unused imports, functions, and fields

- Remove #![allow(dead_code)] from main.rs, fix all revealed warnings
- Delete unused schema_assimilation() from neuro/scoring.rs
- Delete duplicate memory_dir() wrapper from knowledge.rs
- Deduplicate load_prompt: knowledge.rs now calls neuro::load_prompt
- Remove unused timeout field from DigestLevel
- Remove unused imports (regex::Regex, Provenance, AnyView, Write)
- Mark OldEntry fields as #[allow(dead_code)] (needed for deserialization)

Co-Authored-By: ProofOfConcept <poc@bcachefs.org>

poc-memory/src/main.rs

@@ -1,4 +1,4 @@
-#![allow(dead_code)]
+
 // poc-memory: graph-structured memory for AI assistants
 //
 // Authors: ProofOfConcept <poc@bcachefs.org> and Kent Overstreet