[BUG] No ability to force the output file format

[nevmerzhitsky]

Basic information

• Program version: 0.2.8
• Python version: 3.11.9
• Operating system: Linux/Windows

Describe the bug

There is no way to force the output file format. Therefore, the library understands the format wrong if the output file path doesn't match the predefined extension mask.

This makes it impossible to use the library in a context where a programmer cannot control the output path value (it's generated by a third party).

Command/Code used

1. The command used (including the verbose tag, -v):

chat_downloader -v --output ./test.jsonl-temp-suffix URL

Expected behavior

A parameter like --output_format must exist.

Additional context/information

The ContinuousWriter class already supports this functionality, but the library doesn't expose it for clients.