feat(core): promote AuthenticationFailureException + ConnectionAttemptFailedException to public top-level types

Both exceptions used to live as `internal sealed class` definitions nested at
the bottom of ObsWebSocketClient.cs. The library already raises a public
`AuthenticationFailure` event with a public AuthenticationFailureEventArgs, so
the typed signal exists — but consumers that prefer a typed catch over an
event subscription couldn't `catch (AuthenticationFailureException)` because
the type wasn't visible.

Promote both exceptions to public top-level types in their own files,
documented inline. Internal call sites and the existing tests (which already
referenced these by name through InternalsVisibleTo) compile unchanged. The
public AuthenticationFailure event continues to fire for callers that prefer
the event-driven path.

Motivation: downstream consumers (StreamWeaver in particular) used to
string-match exception messages — `Contains("auth")` / `Contains("credential")`
on ObsWebSocketException — which is fragile to library wording changes. With
the typed exception public, those callers can switch to a clean
`catch (AuthenticationFailureException)` or subscribe to the existing
AuthenticationFailure event.

Author: Agash

ObsWebSocket.Core/AuthenticationFailureException.cs

@@ -0,0 +1,35 @@
+namespace ObsWebSocket.Core;
+
+/// <summary>
+/// Thrown when authentication against the OBS WebSocket server fails — typically because the
+/// configured password is wrong, missing, or otherwise rejected by the server's challenge.
+/// </summary>
+/// <remarks>
+/// Consumers can catch this directly to distinguish auth failures from generic
+/// <see cref="ObsWebSocketException"/> connection issues without inspecting the message string.
+/// The same condition is also surfaced via the
+/// <see cref="ObsWebSocketClient.AuthenticationFailure"/> event for callers that prefer the
+/// event-driven path.
+/// </remarks>
+[Serializable]
+public sealed class AuthenticationFailureException : ObsWebSocketException
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="AuthenticationFailureException"/> class.
+    /// </summary>
+    public AuthenticationFailureException() { }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="AuthenticationFailureException"/> class with
+    /// a specified error message.
+    /// </summary>
+    public AuthenticationFailureException(string message)
+        : base(message) { }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="AuthenticationFailureException"/> class with
+    /// a specified error message and a reference to the inner exception that caused this one.
+    /// </summary>
+    public AuthenticationFailureException(string message, Exception? innerException)
+        : base(message, innerException ?? new InvalidOperationException("OBS authentication failed without a more specific cause.")) { }
+}

ObsWebSocket.Core/ConnectionAttemptFailedException.cs

@@ -0,0 +1,30 @@
+namespace ObsWebSocket.Core;
+
+/// <summary>
+/// Thrown when a single connection attempt to the OBS WebSocket server fails for a non-auth
+/// reason — protocol mismatch, transport error, handshake timeout, or a server-rejected
+/// configuration. Distinct from <see cref="AuthenticationFailureException"/> so consumers can
+/// decide whether to retry or stop.
+/// </summary>
+[Serializable]
+public sealed class ConnectionAttemptFailedException : ObsWebSocketException
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ConnectionAttemptFailedException"/> class.
+    /// </summary>
+    public ConnectionAttemptFailedException() { }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ConnectionAttemptFailedException"/> class
+    /// with a specified error message.
+    /// </summary>
+    public ConnectionAttemptFailedException(string message)
+        : base(message) { }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ConnectionAttemptFailedException"/> class
+    /// with a specified error message and a reference to the inner exception that caused this one.
+    /// </summary>
+    public ConnectionAttemptFailedException(string message, Exception? innerException)
+        : base(message, innerException ?? new InvalidOperationException("OBS connection attempt failed without a more specific cause.")) { }
+}

ObsWebSocket.Core/ObsWebSocketClient.cs

@@ -2549,11 +2549,6 @@ private void RaiseAuthenticationFailureEvent(Uri uri, int attempt, Exception err
     }
     #endregion
 
-    #region Internal Exception Types
-    internal sealed class ConnectionAttemptFailedException(string message, Exception? inner = null)
-        : ObsWebSocketException(message, inner);
-
-    internal sealed class AuthenticationFailureException(string message, Exception? inner = null)
-        : ObsWebSocketException(message, inner);
-    #endregion
+    // ConnectionAttemptFailedException and AuthenticationFailureException were promoted to
+    // public top-level types in v0.3.1-dev3; their definitions now live in their own files.
 }