2D Array Slicing

Problem Statement

Extract portions of a 2D NumPy array using slicing.

Background

For 2D arrays:

• arr[i, j] - element at row i, column j
• arr[i, :] or arr[i] - entire row i
• arr[:, j] - entire column j
• arr[r1:r2, c1:c2] - submatrix

Your Task

Write a function slice_2d(arr) that returns a dictionary with:

• "top_left": Top-left 2×2 submatrix (as list)
• "bottom_row": Last row (as list)
• "right_col": Rightmost column (as list)
• "center": Center element (as int, for odd dimensions)