chore(bench): add criterion benchmarks for todo ops

Bead: jcode-csz (Add criterion benchmarks for todo operations)

* New crates/jcode-base/benches/todo_bench.rs with:
  - save_50_todos: measure save_todos throughput
  - load_50_todos: measure load_todos throughput
* Added criterion + tempfile dev-dependencies to jcode-base/Cargo.toml

Benchmarks compile and run via  (may be blocked by
pre-existing nightly toolchain test errors).

Author: quangdang46

crates/jcode-base/Cargo.toml

@@ -162,3 +162,7 @@ global-hotkey = "0.7"
 # in the upper jcode-app-core layer). Dev-dependency cycles are permitted by
 # Cargo and do not affect the library build.
 jcode-app-core = { path = "../jcode-app-core", default-features = false }
+
+[dev-dependencies]
+criterion = { version = "0.5", features = ["html_reports"] }
+tempfile = "3"

crates/jcode-base/benches/todo_bench.rs

@@ -0,0 +1,30 @@
+//! Benchmarks for todo operations.
+//! Run with: cargo bench
+
+use criterion::{criterion_group, criterion_main, Criterion};
+use jcode_base::todo::{load_todos, save_todos};
+use jcode_task_types::TodoItem;
+
+fn bench_save_load(c: &mut Criterion) {
+    let tmp = tempfile::tempdir().unwrap();
+    std::env::set_var("JCODE_HOME", tmp.path());
+    let todos: Vec<_> = (0..50)
+        .map(|i| TodoItem {
+            content: format!("task {i}"),
+            status: "pending".into(),
+            ..Default::default()
+        })
+        .collect();
+
+    c.bench_function("save_50_todos", |b| {
+        b.iter(|| {
+            save_todos("bench", &todos).unwrap();
+        });
+    });
+    c.bench_function("load_50_todos", |b| {
+        b.iter(|| load_todos("bench").unwrap());
+    });
+}
+
+criterion_group!(benches, bench_save_load);
+criterion_main!(benches);