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/ParameterResolver/AssociativeArrayResolver.php

@@ -0,0 +1,37 @@
+<?php declare(strict_types=1);
+
+namespace Invoker\ParameterResolver;
+
+use ReflectionFunctionAbstract;
+
+/**
+ * Tries to map an associative array (string-indexed) to the parameter names.
+ *
+ * E.g. `->call($callable, ['foo' => 'bar'])` will inject the string `'bar'`
+ * in the parameter named `$foo`.
+ *
+ * Parameters that are not indexed by a string are ignored.
+ */
+class AssociativeArrayResolver implements ParameterResolver
+{
+    public function getParameters(
+        ReflectionFunctionAbstract $reflection,
+        array $providedParameters,
+        array $resolvedParameters
+    ): array {
+        $parameters = $reflection->getParameters();
+
+        // Skip parameters already resolved
+        if (! empty($resolvedParameters)) {
+            $parameters = array_diff_key($parameters, $resolvedParameters);
+        }
+
+        foreach ($parameters as $index => $parameter) {
+            if (array_key_exists($parameter->name, $providedParameters)) {
+                $resolvedParameters[$index] = $providedParameters[$parameter->name];
+            }
+        }
+
+        return $resolvedParameters;
+    }
+}