Add support for non-isolated masks

[LaurenzV]

I also measured this using the Blend2D benchmark suite and it doesn't result in in any noticeable slowdown.

[LaurenzV]

I should note it's a bit unfortunate the size of a command increases, but I think if we really want to optimize for that there are other avanues we could explore first (for example the paint field is currently very big since it currently stores the f32 version and u8 version of a color inline. I could also put it behind a feature flag somehow s that at least vello_hybrid is not affected.

[LaurenzV]

I've rebased this onto main now. I also reran the Blend2D benchmark harness, and there does seem to be a slight slowdown in some cases, but nothing worrying (around 1-2%, in extreme cases 3%). It is a bit unfortunate that every command stores an Option now, so maybe there is something better we can do here, but it's probably also not a huge deal either?

[taj-p]

Sorry for the delay. I'll review this over the next couple days

[LaurenzV]

All good, it can wait until after your vacation! Enjoy it!