feat: Add basic project structure and initial crates

- Added basic project structure with workspace and crates:
  `kvstore`, `vault`, `evm_client`, `cli_app`, `web_app`.
- Created initial `Cargo.toml` files for each crate.
- Added placeholder implementations for key components.
- Included initial documentation files (`README.md`, architecture
  docs, repo structure).
- Included initial implementaion for kvstore crate(async API, backend abstraction, separation of concerns, WASM/native support, testability)
- Included native and browser tests for the kvstore crate

kvstore/tests/native.rs

@@ -0,0 +1,33 @@
+#![cfg(not(target_arch = "wasm32"))]
+use kvstore::{NativeStore, KVStore};
+
+#[tokio::test]
+async fn test_native_store_basic() {
+    let tmp_dir = tempfile::tempdir().unwrap();
+    let path = tmp_dir.path().join("testdb");
+    let store = NativeStore::open(path.to_str().unwrap()).unwrap();
+
+    // Test set/get
+    store.set("foo", b"bar").await.unwrap();
+    let val = store.get("foo").await.unwrap();
+    assert_eq!(val, Some(b"bar".to_vec()));
+
+    // Test exists
+    assert_eq!(store.contains_key("foo").await.unwrap(), true);
+    assert_eq!(store.contains_key("bar").await.unwrap(), false);
+    store.remove("foo").await.unwrap();
+    assert_eq!(store.get("foo").await.unwrap(), None);
+
+    // Test keys
+    store.set("foo", b"bar").await.unwrap();
+    store.set("baz", b"qux").await.unwrap();
+    let keys = store.keys().await.unwrap();
+    assert_eq!(keys.len(), 2);
+    assert!(keys.contains(&"foo".to_string()));
+    assert!(keys.contains(&"baz".to_string()));
+
+    // Test clear
+    store.clear().await.unwrap();
+    let keys = store.keys().await.unwrap();
+    assert_eq!(keys.len(), 0);
+}

kvstore/tests/web.rs

@@ -0,0 +1,46 @@
+#![cfg(target_arch = "wasm32")]
+//! WASM/browser tests for kvstore using wasm-bindgen-test
+
+use kvstore::{WasmStore, KVStore};
+use wasm_bindgen_test::*;
+
+wasm_bindgen_test_configure!(run_in_browser);
+
+#[wasm_bindgen_test]
+async fn test_set_and_get() {
+    let store = WasmStore::open("test-db").await.expect("open");
+    store.set("foo", b"bar").await.expect("set");
+    let val = store.get("foo").await.expect("get");
+    assert_eq!(val, Some(b"bar".to_vec()));
+}
+
+#[wasm_bindgen_test]
+async fn test_delete_and_exists() {
+    let store = WasmStore::open("test-db").await.expect("open");
+    store.set("foo", b"bar").await.expect("set");
+    assert_eq!(store.contains_key("foo").await.unwrap(), true);
+    assert_eq!(store.contains_key("bar").await.unwrap(), false);
+    store.remove("foo").await.unwrap();
+    assert_eq!(store.get("foo").await.unwrap(), None);
+}
+
+#[wasm_bindgen_test]
+async fn test_keys() {
+    let store = WasmStore::open("test-db").await.expect("open");
+    store.set("foo", b"bar").await.expect("set");
+    store.set("baz", b"qux").await.expect("set");
+    let keys = store.keys().await.unwrap();
+    assert_eq!(keys.len(), 2);
+    assert!(keys.contains(&"foo".to_string()));
+    assert!(keys.contains(&"baz".to_string()));
+}
+
+#[wasm_bindgen_test]
+async fn test_clear() {
+    let store = WasmStore::open("test-db").await.expect("open");
+    store.set("foo", b"bar").await.expect("set");
+    store.set("baz", b"qux").await.expect("set");
+    store.clear().await.unwrap();
+    let keys = store.keys().await.unwrap();
+    assert_eq!(keys.len(), 0);
+}