updated arange to mgrid in tutorials and references

[mm-aws06]

Issue #, if available:

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Description of changes:

Updated arange to mgrid in tutorials and references

Testing:

Please see detailed unit test requirements in the CONTRIBUTING.md

• The change is covered by numeric check using nki.baremetal
• The change is covered by performance benchmark test using nki.benchmark
• The change is covered by end-to-end integration test

Pull Request Checklist

• I have filled in all the required field in the template
• I have tested locally that all the tests pass
• By submitting this pull request, I confirm that my contribution is made under the terms of the MIT-0 license.

[aws-qieqingy]

Please check the AutoTest error message, this line seems to have indentation error.

[mm-aws06]

fixed indentation and pushed again :)

[mm-aws06]

After reviewing my PR results, there's something I'd like to ask for anyone's opinion on. The changes I made from arange to mgrid in allocated_attention.py are correct (from what I can tell), however the indexing process is different:

arange and mgrid are both used to generate ranges of indices, but they return different shapes and types:
arange(N) returns a 1D array: [0, 1, ..., N-1]
mgrid[0:N, 0:M] returns two 2D arrays: one for row indices, one for column indices, both of shape (N, M)

Should I switch back from mgrid to arange here? Or alter the indexing? (and for the latter, will that involve making changes to the test files as well?)