[ie/mixch] Add comment extraction; update a test

[pzhlkj6612]

IMPORTANT: PRs without the template will be CLOSED

Description of your pull request and other information

info_json:

  "comments": [
    {
      "author": "A",
      "author_id": 42,
      "id": "",  // could be an empty string
      "text": "...",
      "timestamp": 1700000000
    },
    {
      "author": "B",
      "author_id": 43,
      "id": "item-1984",
      "text": "...",
      "timestamp": 1700000001
    },

.

Template

Before submitting a pull request make sure you have:

• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests
• Checked the code with flake8 and ran relevant tests

In order to be accepted and merged into yt-dlp each piece of code must be in public domain or released under Unlicense. Check all of the following options that apply:

• I am the original author of this code and I am willing to release it under Unlicense
• I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence)

What is the purpose of your pull request?

• Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
• New feature (It is strongly recommended to open an issue first)

[pukkandan]

      "id": "",  // could be an empty string

This is not ideal. Is there any other key that could be used as ID?

[pzhlkj6612]

Hi, @pukkandan .

This is not ideal. Is there any other key that could be used as ID?

Unfortunately, there is no such key.

So, should we remove "id"?

[pukkandan]

• It is better to have id=None than id="".
• author_id should be returned as as a str, not int.
• {TYPE_or_none} converts the data into TYPE while {TYPE} verifies the data is TYPE without converting

Considering these, I believe this is the proper impl:

Suggested change

	'author': ('name', {str_or_none}),
	'author_id': ('user_id', {int_or_none}),
	'id': ('message_id', {str_or_none}),
	'text': ('body', {str_or_none}),
	'timestamp': ('created', {int_or_none}),
	'author': ('name', {str}),
	'author_id': ('user_id', {str_or_none}),
	'id': ('message_id', {str}, {lambda x: x or None),
	'text': ('body', {str}),
	'timestamp': ('created', {int}),

Correct?

[pzhlkj6612]

Thanks! I must have been confused "{TYPE_or_none}" and "{TYPE}" at that time.

Fixed in 5bbd6c1.