delete 20 dead public functions across 12 files

Removed functions with zero callers: parse_timestamp_to_epoch,
hash_key, search_weighted_debug, extract_query_terms, format_results,
move_to_neighbor, adjust_edge_strength, update_graph_metrics,
nearest_to_seeds, nystrom_project, chat_completion_stream, cmd_read,
context_message, split_candidates, split_plan_prompt,
split_extract_prompt, log_event_pub, log_verbose, rpc_record_hits,
memory_definitions. -245 lines.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/hippocampus/lookups.rs

@@ -197,8 +197,3 @@ pub fn dump_resolved(date: &str, keys: &[String]) -> Result<Vec<(String, u32)>,
 
     Ok(resolved)
 }
-
-/// Hash a key (exposed for testing/external use).
-pub fn hash_key(key: &str) -> u64 {
-    fnv1a(key)
-}