Integrate TransformProgram with QNode

[albi3ro]

This PR integrates the TransformProgram with both the QNode and qml.execute.

[rmoyard]

Hi @albi3ro, thanks for the PR. The transform rework is also a project to bring us closer to catalyst and eventually to be able to execute a hybrid program execute(program). I would suggest to follow what we accepted in the PRD/ADR and add the program to the execution function.

[albi3ro]

looks super clean 🎉 just one thought: do we want to advertise using partial when decorating a qnode with a transform? I know decorator syntax makes it tough, but I wonder if we can make this better for users without compromising code quality too much

ps: did you mean to delete the specs test (seeing as they're marked to fail)?

Yep. Just going through the qnode tests I realized that the qnode no longer has a specs property.

There will be two ways of adding a transform to the qnode:

@partial(my_transform, kwarg = value)
@qml.qnode(dev)
def circuit():

Or

circuit = my_transform(circuit, kwarg=value)

This way we're always dispatching on the first argument to the transform call.

[rmoyard]

Thanks it looks good 👍 There is just one test to correct

[timmysilv]

I'm still unsure about advertising using partial - I know it's "correct" in that the code is cleaner, but I fear that it will discourage/confuse users (which is why we made a mess of all that type-checking the first time around - slimy, yet satisfying! 🐛)

anyway, this PR is blocking Romain and that change can be made later if needed. Approved!