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/enrich.rs

@@ -11,7 +11,6 @@ use crate::llm::{call_sonnet, parse_json_response, semantic_keys};
 use crate::neuro;
 use crate::store::{self, Store, new_node, new_relation};
 
-use regex::Regex;
 use std::collections::hash_map::DefaultHasher;
 use std::collections::HashSet;
 use std::fs;