Rewrite email parser using ImapEngine, harden processing loop

Replace webklex/php-imap with directorytree/imapengine in the ticket
email parser. ImapEngine is pure PHP over sockets.

Parser improvements:
- Wrap per-message processing in try/catch so one malformed email
  can't abort the run; failures are flagged and logged with UID
- Query unseen + unflagged so previously-failed (flagged) messages
  are no longer re-processed on every cron run
- Skip vacation/auto-responder emails (RFC 3834) to prevent mail
  loops with the ticket auto-reply
- Cap messages per run (50) and attachment size (15MB); inline
  images over 2MB are stored as attachments instead of base64-embedded
  in ticket details
- Atomic lock file creation
- preg_quote() the ticket prefix in subject matching
- Dedupe CC watchers and exclude the sender
- Map webklex 'tls' encryption setting to STARTTLS for compatibility

NDR/DSN parsing now walks MIME parts via the underlying
zbateson parser instead of relying on attachment extraction.

plugins/vendor/php-di/invoker/src/Exception/InvocationException.php

@@ -0,0 +1,10 @@
+<?php declare(strict_types=1);
+
+namespace Invoker\Exception;
+
+/**
+ * Impossible to invoke the callable.
+ */
+class InvocationException extends \Exception
+{
+}

plugins/vendor/php-di/invoker/src/Exception/NotCallableException.php

@@ -0,0 +1,33 @@
+<?php declare(strict_types=1);
+
+namespace Invoker\Exception;
+
+/**
+ * The given callable is not actually callable.
+ */
+class NotCallableException extends InvocationException
+{
+    /**
+     * @param mixed $value
+     */
+    public static function fromInvalidCallable($value, bool $containerEntry = false): self
+    {
+        if (is_object($value)) {
+            $message = sprintf('Instance of %s is not a callable', get_class($value));
+        } elseif (is_array($value) && isset($value[0], $value[1])) {
+            $class = is_object($value[0]) ? get_class($value[0]) : $value[0];
+
+            $extra = method_exists($class, '__call') || method_exists($class, '__callStatic')
+                ? ' A __call() or __callStatic() method exists but magic methods are not supported.'
+                : '';
+
+            $message = sprintf('%s::%s() is not a callable.%s', $class, $value[1], $extra);
+        } elseif ($containerEntry) {
+            $message = var_export($value, true) . ' is neither a callable nor a valid container entry';
+        } else {
+            $message = var_export($value, true) . ' is not a callable';
+        }
+
+        return new self($message);
+    }
+}

plugins/vendor/php-di/invoker/src/Exception/NotEnoughParametersException.php

@@ -0,0 +1,10 @@
+<?php declare(strict_types=1);
+
+namespace Invoker\Exception;
+
+/**
+ * Not enough parameters could be resolved to invoke the callable.
+ */
+class NotEnoughParametersException extends InvocationException
+{
+}