add __all__ to cofunction.py

[dham]

This was causing namespace leakage into the main firedrake namespace.

fixes #4696.

[connorjward]

Shouldn't this go into release?

[dham]

Shouldn't this go into release?

Good question. Technically it's an API change and someone's code might depend on Firedrake exposing np.

[connorjward]

Shouldn't this go into release?

Good question. Technically it's an API change and someone's code might depend on Firedrake exposing np.

Fair enough. Sometimes it's hard to decide exactly where the line is.

[connorjward]

This appears to be causing a lot of failures. It's not just np that is accidentally getting exported I think.

[leo-collins]

The files inside firedrake/external_operators are also missing __all__

[sghelichkhani]

Good question. Technically it's an API change and someone's code might depend on Firedrake exposing np.

This will break our demo rendering on gadopt exactly for this reason.

But it's something we needed to fix on our side anyways. So happy with whatever happens.