Updated atom_arrangement.py

[AbdullahKazi500]

Issue #, if available:
fixes #969
Description of changes:
defined the SiteType enum and AtomArrangementItem dataclass to handle the coordinates and site types, ensuring validations.
AtomArrangement Class:
The class initializes with an empty list of sites.
Add Method: Adds a coordinate to the arrangement with a site type.
Retrieves a list of coordinates for a given index.
Rounds coordinates to the nearest multiple of the given resolution.
Factory Methods: Methods for creating square and rectangular lattice arrangements. Demonstrates creating a square lattice with specified boundary points and lattice constant.
Testing done:
will be adding the test

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[peterkomar-aws]

Please consolidate the work to this PR: #989