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/Cargo.toml

@@ -0,0 +1,31 @@
+[package]
+name = "kvstore"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+path = "src/lib.rs"
+
+[dependencies]
+async-trait = "0.1"
+sled = { version = "0.34", optional = true }
+idb = { version = "0.4", optional = true }
+js-sys = "0.3"
+wasm-bindgen = "0.2"
+wasm-bindgen-futures = "0.4"
+thiserror = "1"
+tempfile = "3"
+
+[features]
+default = []
+native = ["sled", "tokio"]
+web = ["idb"]
+
+[target.'cfg(not(target_arch = "wasm32"))'.dependencies]
+tokio = { version = "1.45", optional = true, default-features = false, features = ["rt-multi-thread", "macros"] }
+
+[target.'cfg(target_arch = "wasm32")'.dependencies]
+idb = "0.4"
+
+[target.'cfg(target_arch = "wasm32")'.dev-dependencies]
+wasm-bindgen-test = "0.3"