Fix list_topics crash on Telethon 1.42

[embogomolov]

What's broken

Telethon 1.42 doesn't generate a Python wrapper for the channels.getForumTopics TL method. Calling functions.channels.GetForumTopicsRequest(...) in list_topics throws an AttributeError because the class simply doesn't exist in this version.

The fix

Hand-wrote the TL request class (GetForumTopicsRequest) following the schema:

channels.getForumTopics#de560d1 flags:# channel:InputChannel
    q:flags.0?string offset_date:int offset_id:int
    offset_topic:int limit:int = messages.ForumTopics;

It extends TLRequest, handles binary serialization manually via struct.pack, and supports the optional q (search query) flag. Replaces the missing auto-generated class in the list_topics call.

How to test

• Pick a supergroup with forum topics enabled, call list_topics with its ID
• Try with and without search_query parameter

[embogomolov]

Anyone?

[chigwell]

Hey @embogomolov, thank you for the contribution! Could I please ask you to fix the black formatting so the CI tests will pass? Thank you!