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.

docs/vault.md

@@ -0,0 +1,164 @@
+🧱 Vault Crate Architecture
+1. VaultStore
+Purpose: Central manager for all keyspaces.
+
+Responsibilities:
+
+Maintain metadata about keyspaces.
+
+Provide interfaces to create, load, and manage keyspaces.
+
+Ensure each keyspace is encrypted with its own password.
+
+2. KeySpace
+Purpose: Isolated environment containing multiple keypairs.
+
+Responsibilities:
+
+Securely store and manage keypairs.
+
+Provide cryptographic operations like signing and encryption.
+
+Handle encryption/decryption using a password-derived key.
+
+3. KeyPair
+Purpose: Represents an individual cryptographic keypair.
+
+Responsibilities:
+
+Perform cryptographic operations such as signing and verification.
+
+Support key export and import functionalities.
+
+4. Symmetric Encryption Module
+Purpose: Provides encryption and decryption functionalities.
+
+Responsibilities:
+
+Encrypt and decrypt data using algorithms like ChaCha20Poly1305.
+
+Derive encryption keys from passwords using PBKDF2.
+
+5. SessionManager
+Purpose: Manages the active context for cryptographic operations, simplifying API usage.
+
+Responsibilities:
+
+Maintain the currently selected keypair.
+
+Provide simplified methods for cryptographic operations without repeatedly specifying the keypair.
+
+🔐 Security Model
+Per-KeySpace Encryption: Each keyspace is encrypted independently using a key derived from its password.
+
+VaultStore Metadata: Stores non-sensitive metadata about keyspaces, such as their names and creation dates. This metadata can be stored in plaintext or encrypted based on security requirements.
+
+🧪 API Design
+VaultStore
+rust
+Copy
+Edit
+pub struct VaultStore {
+    // Internal fields
+}
+
+impl VaultStore {
+    pub fn new() -> Self;
+    pub fn load() -> Result<Self, VaultError>;
+    pub fn save(&self) -> Result<(), VaultError>;
+
+    pub fn list_keyspaces(&self) -> Vec<KeyspaceMetadata>;
+    pub fn create_keyspace(&mut self, name: &str, password: &str) -> Result<(), VaultError>;
+    pub fn delete_keyspace(&mut self, name: &str) -> Result<(), VaultError>;
+    pub fn rename_keyspace(&mut self, old_name: &str, new_name: &str) -> Result<(), VaultError>;
+    pub fn load_keyspace(&self, name: &str, password: &str) -> Result<KeySpace, VaultError>;
+}
+KeySpace
+rust
+Copy
+Edit
+pub struct KeySpace {
+    // Internal fields
+}
+
+impl KeySpace {
+    pub fn new(name: &str, password: &str) -> Result<Self, VaultError>;
+    pub fn save(&self) -> Result<(), VaultError>;
+
+    pub fn list_keypairs(&self) -> Vec<String>;
+    pub fn create_keypair(&mut self, name: &str) -> Result<(), VaultError>;
+    pub fn delete_keypair(&mut self, name: &str) -> Result<(), VaultError>;
+    pub fn rename_keypair(&mut self, old_name: &str, new_name: &str) -> Result<(), VaultError>;
+    pub fn get_keypair(&self, name: &str) -> Result<KeyPair, VaultError>;
+
+    pub fn sign(&self, keypair_name: &str, message: &[u8]) -> Result<Vec<u8>, VaultError>;
+    pub fn verify(&self, keypair_name: &str, message: &[u8], signature: &[u8]) -> Result<bool, VaultError>;
+}
+KeyPair
+rust
+Copy
+Edit
+pub struct KeyPair {
+    // Internal fields
+}
+
+impl KeyPair {
+    pub fn new() -> Self;
+    pub fn from_private_key(private_key: &[u8]) -> Result<Self, VaultError>;
+
+    pub fn public_key(&self) -> Vec<u8>;
+    pub fn private_key(&self) -> Vec<u8>;
+
+    pub fn sign(&self, message: &[u8]) -> Result<Vec<u8>, VaultError>;
+    pub fn verify(&self, message: &[u8], signature: &[u8]) -> Result<bool, VaultError>;
+}
+SessionManager (Optional)
+rust
+Copy
+Edit
+pub struct SessionManager {
+    keyspace: KeySpace,
+    active_keypair: String,
+}
+
+impl SessionManager {
+    pub fn new(keyspace: KeySpace, keypair_name: &str) -> Result<Self, VaultError>;
+    pub fn sign(&self, message: &[u8]) -> Result<Vec<u8>, VaultError>;
+    pub fn verify(&self, message: &[u8], signature: &[u8]) -> Result<bool, VaultError>;
+    pub fn switch_keypair(&mut self, keypair_name: &str) -> Result<(), VaultError>;
+}
+📦 Storage Structure
+Copy
+Edit
+vault_store/
+├── metadata.json
+└── keyspaces/
+    ├── alice.ksp
+    ├── bob.ksp
+    └── ...
+metadata.json: Contains metadata about each keyspace, such as name and creation date.
+
+keyspaces/: Directory containing encrypted keyspace files.
+
+🔄 Integration with kvstore
+Native Environment
+Storage Backend: Utilize the local filesystem or a persistent database (e.g., SQLite) for storing VaultStore and KeySpace data.
+
+Usage:
+
+Initialize VaultStore and load existing keyspaces.
+
+Perform cryptographic operations using KeySpace and KeyPair.
+
+Persist changes to disk or database.
+
+Browser Environment (WASM)
+Storage Backend: Use browser storage APIs like localStorage or IndexedDB for persisting data.
+
+Usage:
+
+Compile the vault crate to WebAssembly.
+
+Interact with the vault API through JavaScript bindings.
+
+Store and retrieve encrypted keyspaces using browser storage.