gh-69093: Expose sqlite3.Blob as a class

[JelleZijlstra]

I noticed this was missing while writing typeshed stubs. It's
useful to expose it for use in annotations.

GH-69093

[JelleZijlstra]

Skipping news because this is a simple followup for #30680, which was merged just now.

[erlend-aasland]

I don't use typing, but I guess this is ok.

BTW, we need to disallow instantiation for blob types. I should've thought about that in the first place, but with this change it's even more important. We can embed that change here, or do it in another PR; I'm fine with both.

[JelleZijlstra]

Thanks! Also I don't think it's useful only for annotations: we also mention this class in the docs as if it is accessible, and it's useful for interactive exploration if you can do dir(sqlite3.Blob).

[erlend-aasland]

Thanks! Also I don't think it's useful only for annotations: we also mention this class in the docs as if it is accessible, and it's useful for interactive exploration if you can do dir(sqlite3.Blob).

Good point!