feat: Refactor kvstore and vault to use features and logging

- Remove hardcoded dependencies in kvstore Cargo.toml; use features
  instead. This allows for more flexible compilation for different
  targets (native vs. WASM).
- Improve logging in vault crate using the `log` crate. This makes
  debugging easier and provides more informative output during
  execution.  Native tests use `env_logger`, WASM tests use
  `console_log`.
- Update README to reflect new logging best practices.
- Add cfg attributes to native and wasm modules to improve clarity.
- Update traits.rs to specify Send + Sync behavior expectations.

vault/Cargo.toml

@@ -18,7 +18,10 @@ chacha20poly1305 = "0.10"
 k256 = { version = "0.13", features = ["ecdsa"] }
 ed25519-dalek = "2.1"
 rand_core = "0.6"
+log = "0.4"
 thiserror = "1"
+env_logger = "0.11"
+console_log = "1"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1.0"
 hex = "0.4"