fix: support 64-bit eye on GPU

[aaishwarymishra]

Proposed changes

Please include a description of the problem or feature this PR is addressing. If there is a corresponding issue, include the issue #.
This pull request updates the eye function to improve support for 64-bit data types and adds corresponding tests to ensure correct behavior. The main changes include handling for 64-bit integer types in the implementation and new test cases for these types.

Enhanced dtype support:

• Updated the eye function in mlx/ops.cpp to handle 64-bit data types by constructing the eye matrix as float32 and then converting it to the requested 64-bit type. This ensures compatibility with int64 and uint64 dtypes.

Testing improvements:

• Added test cases in python/tests/test_ops.py to verify that mx.eye correctly returns arrays of int64 and uint64 dtypes.

closes #4300

Checklist

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• I have read the CONTRIBUTING document
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• I have added tests that prove my fix is effective or that my feature works
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