🎶 Add support for chords

[Felienne]

Fixes #4964

How to test

Follow these steps to verify this PR works as intended:

• Try play C4 D4 E4 from level 3
• I also added a few tests

Checklist Done? Check if you have it all in place using this list: (mark with x if done)

• [X] Contains one of the PR categories in the name
• [X] Describes changes in the format above
• [X] Links to an existing issue or discussion
• [X] Has a "How to test" section

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