Update dependencies and add new features for improved functionality

- Updated Cargo.lock and Cargo.toml to include new dependencies
- Added new files for backup and watcher functionality in libmarlin
- Introduced integration tests and documentation updates
- Set workspace resolver to version 2 for better dependency resolution

libmarlin/src/error.rs

@@ -0,0 +1,68 @@
+//! Error types for Marlin
+//!
+//! This module defines custom error types used throughout the application.
+
+use std::io;
+use std::fmt;
+
+/// Result type for Marlin - convenience wrapper around Result<T, Error>
+pub type Result<T> = std::result::Result<T, Error>;
+
+/// Custom error types for Marlin
+#[derive(Debug)]
+pub enum Error {
+    /// An IO error
+    Io(io::Error),
+    
+    /// A database error
+    Database(String),
+    
+    /// An error from the notify library
+    Watch(String),
+    
+    /// Invalid state for the requested operation
+    InvalidState(String),
+    
+    /// Path not found
+    NotFound(String),
+    
+    /// Invalid configuration
+    Config(String),
+    
+    /// Other errors
+    Other(String),
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Io(err) => write!(f, "IO error: {}", err),
+            Self::Database(msg) => write!(f, "Database error: {}", msg),
+            Self::Watch(msg) => write!(f, "Watch error: {}", msg),
+            Self::InvalidState(msg) => write!(f, "Invalid state: {}", msg),
+            Self::NotFound(path) => write!(f, "Not found: {}", path),
+            Self::Config(msg) => write!(f, "Configuration error: {}", msg),
+            Self::Other(msg) => write!(f, "Error: {}", msg),
+        }
+    }
+}
+
+impl std::error::Error for Error {}
+
+impl From<io::Error> for Error {
+    fn from(err: io::Error) -> Self {
+        Self::Io(err)
+    }
+}
+
+impl From<rusqlite::Error> for Error {
+    fn from(err: rusqlite::Error) -> Self {
+        Self::Database(err.to_string())
+    }
+}
+
+impl From<notify::Error> for Error {
+    fn from(err: notify::Error) -> Self {
+        Self::Watch(err.to_string())
+    }
+}