[ie/radiko]add Metadata info (performer, duration)

[YoshichikaAAA]

IMPORTANT: PRs without the template will be CLOSED

Description of your pull request and other information

Adds the following information as metadata that can be obtained from radiko.jp for the target program:

• Performers
• Duration

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]

• (Make sure to add/update tests)

[YoshichikaAAA]

• (Make sure to add/update tests)

This site (radiko.jp) provides Japanese radio programs with live streaming and on-demand.
The metadata for live streaming, such as performer, program duration, dynamically changes depending on the time of execution.
Additionally, on-demand streaming is available for only one week after the broadcast.
Furthermore, it is only accessible within Japan, and channels available for viewing are exclusive to each prefecture determined by IP addresses.

In the original source code, the tests specifically target URL detection only.
Considering it will be executed in CI, creating tests beyond the current scope is difficult.