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

.gitignore

@@ -0,0 +1,7 @@
+# Ignore target directory
+/target/
+# Ignore Cargo.lock for libraries
+**/Cargo.lock
+# Ignore IDE files
+.idea/
+.vscode/