Add an optional callback trait which can be implemented and provided to most flashing functions

[jessebraham]

Hopefully this will make espflash a bit more usable as a library.

@bugadani does this seem reasonable enough to you? Would love to hear any feedback you might have.

I suppose this is sort of an extension of #283 as well, so @svenstaro will this still work for your use case as well? Sorry for changing this again 😁

Closes #310.

[bugadani]

Thanks!

This looks awesome, although I have two small comments:

• I think you might want to pass in the impl ProgressCallbacks type by value. I think that if I really need a reference to some object, I might implement the trait for the reference myself. Explicitly borrowing sounds a bit unnecessary to me.
• I think I would replace the optional arguments with an empty ProgressCallbacks implementation, which would allow cleaning up some of the progress report sites (like write_segment). Although, I don't know if this would be a good idea or a complete antipattern instead 🤷‍♂️

[svenstaro]

Should be fine for my purposes. Certainly improves the API.

[jessebraham]

@bugadani I briefly poked at this and tried to get it working with impl ProgressCallbacks but I kept running into issues regarding object safety. I am pretty busy with other projects right now so I can't really spend much time on this for a bit. If you're able to build on top of this that'd be great; otherwise, whenever I get back to it I will either update it myself or just merge it as-is. Even though the API isn't ideal it does at least work in its current form.

[bugadani]

Oh, please don't feel like my comments are anything more than mere wishes. I'm pretty happy with the PR as is :)

[jessebraham]

Okay, glad to hear that. In that case I'm just going to merge this I suppose, we still have the opportunity to tweak it if needed.