feat: add methods to append errors from list of ErrorOr to current

wip, this is only the basic implementation.
ToDo:
- AppendErrors with ErrorOrs of same type using generics
- AppendErrors to `Task<ErrorOr>`
- Tests :)

Refs: amantinband#120

src/ErrorOr/ErrorOr.AppendErrors.cs

@@ -0,0 +1,20 @@
+namespace ErrorOr;
+
+public readonly partial record struct ErrorOr<TValue> : IErrorOr<TValue>
+{
+    /// <summary>
+    /// If the state is error or any of the given <paramref name="errorOrs"/> has errors, an <see cref="ErrorOr"/> instance with all errors of the given instances will be returned.
+    /// </summary>
+    /// <param name="errorOrs">The <see cref="ErrorOr"/> instances which errors should be added to the result.</param>
+    /// <returns>The original <see cref="Value"/> if all states are value, otherwise a list of all errors.</returns>
+    public ErrorOr<TValue> AppendErrors(params IErrorOr[] errorOrs)
+    {
+        List<Error> combinedErrors = ErrorsOrEmptyList;
+        foreach (IErrorOr errorOr in errorOrs)
+        {
+            combinedErrors.AddRange(errorOr.Errors ?? []);
+        }
+
+        return combinedErrors.Count == 0 ? this : combinedErrors;
+    }
+}

src/ErrorOr/ErrorOr.AppendErrorsExtensions.cs

@@ -0,0 +1,21 @@
+namespace ErrorOr;
+
+public static partial class ErrorOrExtensions
+{
+    /// <summary>
+    /// If the state of <paramref name="original"/> is error or any of the given <paramref name="errorOrs"/> has errors, an <see cref="ErrorOr"/> instance with all errors of the given instances will be returned.
+    /// </summary>
+    /// <param name="original">The <see cref="ErrorOr"/> instance which value should be returned on success.</param>
+    /// <param name="errorOrs">The <see cref="ErrorOr"/> instances which errors should be added to the result.</param>
+    /// <returns>The value of <paramref name="original"/> if all states are value, otherwise a list of all errors.</returns>
+    public static ErrorOr<TValue> AppendErrors<TValue>(this ErrorOr<TValue> original, params IErrorOr[] errorOrs)
+    {
+        List<Error> combinedErrors = original.ErrorsOrEmptyList;
+        foreach (IErrorOr errorOr in errorOrs)
+        {
+            combinedErrors.AddRange(errorOr.Errors ?? []);
+        }
+
+        return combinedErrors.Count == 0 ? original : combinedErrors;
+    }
+}