clippy: fix all warnings across all binaries

- &PathBuf → &Path in memory-search.rs signatures
- Redundant field name in graph.rs struct init
- Add truncate(false) to lock file open
- Derive Default for Store instead of manual impl
- slice::from_ref instead of &[x.clone()]
- rsplit_once instead of split().last()
- str::repeat instead of iter::repeat().take().collect()
- is_none_or instead of map_or(true, ...)
- strip_prefix instead of manual slicing

Zero warnings on `cargo clippy`.

src/bin/memory-search.rs

@@ -10,7 +10,7 @@
 use std::collections::HashSet;
 use std::fs;
 use std::io::{self, Read, Write};
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use std::process::Command;
 
 fn main() {
@@ -138,7 +138,7 @@ fn extract_key_from_line(line: &str) -> Option<String> {
     }
 }
 
-fn load_or_create_cookie(dir: &PathBuf, session_id: &str) -> String {
+fn load_or_create_cookie(dir: &Path, session_id: &str) -> String {
     let path = dir.join(format!("cookie-{}", session_id));
     if path.exists() {
         fs::read_to_string(&path).unwrap_or_default().trim().to_string()
@@ -165,7 +165,7 @@ fn generate_cookie() -> String {
         .collect()
 }
 
-fn load_seen(dir: &PathBuf, session_id: &str) -> HashSet<String> {
+fn load_seen(dir: &Path, session_id: &str) -> HashSet<String> {
     let path = dir.join(format!("seen-{}", session_id));
     if path.exists() {
         fs::read_to_string(path)
@@ -178,7 +178,7 @@ fn load_seen(dir: &PathBuf, session_id: &str) -> HashSet<String> {
     }
 }
 
-fn mark_seen(dir: &PathBuf, session_id: &str, key: &str) {
+fn mark_seen(dir: &Path, session_id: &str, key: &str) {
     let path = dir.join(format!("seen-{}", session_id));
     if let Ok(mut f) = fs::OpenOptions::new().create(true).append(true).open(path) {
         writeln!(f, "{}", key).ok();