#1139 Limit the size of fetched remote files

Today

• RemoteImage, RemoteDocument, RemoteAudio and RemoteVideo download the full file before they inline or upload it.
• The download has no size limit, and a compressed body expands with no limit.

Problem

• A very large file fills worker memory and temporary storage.
• The request then fails late, with a memory error instead of a clear message.

Change

• A download stops at 100 MB and throws an InvalidArgumentException that names the limit.
• A file whose Content-Length is over the limit fails before the body downloads.
• The limit counts the decoded bytes, so compressed bodies are limited too.

[!NOTE]
Remote files over 100 MB now throw. Set ai.remote_files.max_size (in kilobytes) to change the limit.