Add getter and setter for channel label/type/units to a StreamInfo

[mscheltienne]

From mne-lsl, slightly stepped down in term of error checking on the input, this PR adds the methods:

• get_channel_labels
• get_channel_types
• get_channel_units
• set_channel_labels
• set_channel_types
• set_channel_units

to a StreamInfo, to easily interact and add those basic informations to the XMLElement object.

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Also ran black, isort, and codespell to improve and standardize the code-style. Those commits can be reverted if you prefer.

[cboulay]

I'm sorry I slept on this. It looks good, thank you! I personally prefer properties over getters and setters, but I think it works in this case the getter is better because the XML access is fairly slow and we don't want auto-inspection of these properties. Also using a method hints to the user that it will not return immediately, unlike a property where that might be expected.