Merge main into refactor, resolve Runtime.php conflict

Main added new runtimes as class constants; our refactor converted
Runtime to a backed enum. Kept the enum format with all runtimes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: aarondfrancis

src/Results/SettledResult.php

@@ -40,7 +40,7 @@ public function __construct(
      */
     public function isError()
     {
-        return $this->raw->get('FunctionError') !== '';
+        return $this->raw->hasKey('FunctionError') && $this->raw->get('FunctionError') !== '';
     }
 
     /**
@@ -79,15 +79,15 @@ public function toResponse(mixed $request)
      *
      * @throws Exception
      */
-    public function throw(?int $numberOfBacktraces)
+    public function throw(?int $numberOfBacktraces = null)
     {
         if (!$this->isError()) {
             return $this;
         }
 
         throw new LambdaExecutionException(sprintf('Lambda Execution Exception for %s: "%s".', ...[
             get_class($this->function),
-            $this->errorAsString($numberOfBacktraces)
+            $this->errorAsString($numberOfBacktraces ?? 2)
         ]));
     }