Refactor entire codebase and rewrite documentation

Sources/DataLiteCore/Structures/SQLiteError.swift

@@ -0,0 +1,69 @@
+import Foundation
+import DataLiteC
+
+/// A structure that represents an error produced by SQLite operations.
+///
+/// `SQLiteError` encapsulates both the numeric SQLite error code and its associated human-readable
+/// message. It provides a unified way to report and inspect failures that occur during database
+/// interactions.
+///
+/// - SeeAlso: [Result and Error Codes](https://sqlite.org/rescode.html)
+///
+/// ## Topics
+///
+/// ### Instance Properties
+///
+/// - ``code``
+/// - ``message``
+/// - ``description``
+///
+/// ### Initializers
+///
+/// - ``init(code:message:)``
+public struct SQLiteError: Error, Equatable, CustomStringConvertible, Sendable {
+    /// The extended SQLite result code associated with the error.
+    ///
+    /// This numeric value identifies the specific type of error that occurred. Extended result
+    /// codes offer more precise information than primary codes, enabling finer-grained error
+    /// handling and diagnostics.
+    ///
+    /// - SeeAlso: [Result and Error Codes](https://sqlite.org/rescode.html)
+    public let code: Int32
+    
+    /// The human-readable message returned by SQLite.
+    ///
+    /// This string describes the error condition reported by SQLite. It is typically retrieved
+    /// directly from the database engine and may include details about constraint violations,
+    /// syntax errors, I/O issues, or resource limitations.
+    ///
+    /// - Note: The content of this message is determined by SQLite and may vary between error
+    ///   occurrences. Always refer to this property for detailed diagnostic information.
+    public let message: String
+    
+    /// A textual representation of the error including its code and message.
+    ///
+    /// The value of this property is a concise string describing the error. It includes the type
+    /// name (`SQLiteError`), the numeric code, and the corresponding message, making it useful for
+    /// debugging, logging, or diagnostic displays.
+    public var description: String {
+        "\(Self.self) code: \(code) message: \(message)"
+    }
+    
+    /// Creates a new error instance with the specified result code and message.
+    ///
+    /// Use this initializer to represent an SQLite error explicitly by providing both the numeric
+    /// result code and the associated descriptive message.
+    ///
+    /// - Parameters:
+    ///   - code: The extended SQLite result code associated with the error.
+    ///   - message: A human-readable description of the error, as reported by SQLite.
+    public init(code: Int32, message: String) {
+        self.code = code
+        self.message = message
+    }
+    
+    init(_ connection: OpaquePointer) {
+        self.code = sqlite3_extended_errcode(connection)
+        self.message = String(cString: sqlite3_errmsg(connection))
+    }
+}