Preallocate tiles numpy

[pvrraju]

PR replaces nested list pre-allocation with NumPy arrays for tiles. The change:

1. Uses np.empty(shape, dtype=object) instead of nested list comprehensions
2. Updates array access pattern from tiles[i][j][k] to tiles[i, j, k]
   These changes improve code readability and may provide a slight performance enhancement.

[alxmrs]

I think your commit history is a bit polluted -- it looks like you have the lazy loading PR here also. Mind cleaning that up before I provide a review?

[jdbcode]

@pvrraju it seems this and #253 are conflated. I've documented the preallocation as a feature request and linked to this PR in issue #280 so we have a record of the proposed implementation. I'm going close this. Before opening a new pull request with the change, can you please wait until #275 is in a pre or stable release. It's a major refactor that may affect the implementation and almost certainly the location of the changes you'll make. Thanks for your patience.