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/store/persist.rs

@@ -16,7 +16,7 @@ use capnp::serialize;
 
 use std::collections::HashMap;
 use std::fs;
-use std::io::{BufReader, BufWriter, Seek, Write as IoWrite};
+use std::io::{BufReader, BufWriter, Seek};
 use std::path::Path;
 
 impl Store {