feat: implement content cache

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

lib/Client/Message.php

@@ -16,6 +16,7 @@ final class Message
      * @param list<MessageAddress> $bcc
      * @param array<string, string> $bodySections
      * @param list<string> $references message ids from the References header, without angle brackets
+     * @param list<string> $truncatedSections part ids of text sections cut off by a partial fetch
      */
     public function __construct(
         private readonly int $sequence,
@@ -37,6 +38,7 @@ final class Message
         private readonly ?MessagePart $bodyStructure,
         private readonly array $bodySections,
         private readonly array $references = [],
+        private readonly array $truncatedSections = [],
     ) {}
 
     public function sequence(): int
@@ -166,6 +168,16 @@ final class Message
         return $this->bodySections;
     }
 
+    /**
+     * Part ids of text sections that were cut off by a partial fetch.
+     *
+     * @return list<string>
+     */
+    public function truncatedSections(): array
+    {
+        return $this->truncatedSections;
+    }
+
     public function bodyRaw(): ?string
     {
         return $this->bodySections[''] ?? null;
@@ -196,6 +208,7 @@ final class Message
             $bodyStructure,
             $bodySections,
             $this->references,
+            $this->truncatedSections,
         );
     }
 }