Rename qml.numpy from np to pnp

[JerryChen97]

Context:
Too many places where we import pennylane.numpy as np or from pennylane import numpy as np, which is very confusing and conflicting with common import numpy as np. The standard is either pnp (prefered), qnp or anp.

Description of the Change:
Change most of np to pnp. In one file there's npp also changed to pnp

Benefits:
Less confusion. More standardization.

Possible Drawbacks:
How do we deal with docstr and docs?

Related GitHub Issues:

[github-actions]

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Please edit doc/releases/changelog-dev.md with:

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Additional details and impacted files

@@            Coverage Diff            @@
##             master    #6723   +/-   ##
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  Coverage          ?   99.62%           
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  Files             ?      474           
  Lines             ?    44628           
  Branches          ?        0           
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  Hits              ?    44459           
  Misses            ?      169           
  Partials          ?        0           

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[josh146]

How do we deal with docstr and docs?

For docstring and docs, we have a long standing convention of

from pennylane import numpy as np

and this is what almost all users use.

For now, let's leave user facing docs in this form -- we can re-evaluate when we push on removing autograd.