fix keraslayer set and get attr dunders

[timmysilv]

Context:
Fixes #4999. We re-implemented the default setattr and getattr dunders for KerasLayer (needed to modify the QNode saved on the layer) but we should have called super(), because keras.layer.Layer has its own custom implementation that we needed to use. Our TorchLayer already calls super in these cases.

Note - our existing tests were passing because the weights used had custom names ("w1", "w2", etc.), and this issue only comes up when your weights are named "weights" (which is a rather common case, I'm sure).

Description of the Change:

• Replace our default-handling of get/set-attr dunders with a call to super()
• add a test case matching the one in the bug report using the "weights" identifier

Benefits:
Models using KerasLayer can be saved and loaded properly!

Possible Drawbacks:
N/A

Related GitHub Issues:
Reported initially in #4999, same as #4611 but for Keras

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (v0.34.0-rc0@30a4634). Click here to learn what that means.

Additional details and impacted files

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