Add TryFrom<u8> Implementation for ZoomLevel

[hiratara]

Hello,

In my project, I’m using u8 values to represent zoom levels for a slippy map, as this makes it straightforward to increment ( zoom += 1 ), decrement, or specify zoom levels directly using raw integers, such as from command-line arguments ( myapp --zoom=12 ).

However, I noticed that ZoomLevel currently lacks a way to be constructed directly from a raw u8 value. To address this, I’ve implemented the TryFrom<u8> trait for ZoomLevel, allowing for conversions like:

let zoom: ZoomLevel = 12u8.try_into()?;

Additionally, I’ve introduced a new macro, generate_zoom_level, to simplify the boilerplate code involved in defining the ZoomLevel enum. This macro makes it easier to manage and extend the enum when dealing with large ranges of zoom levels.

I hope you find this contribution useful, and I look forward to your feedback.

[edouardpoitras]

Looks good to me. Thanks!