Build_disk_index from Iterator

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The documentation of `build_disk_index` states:

> This function will construct a DiskANN disk index. Disk indices are ideal for very large datasets that are too large to fit in memory.

However, it only accepts
1) Numpy array: Which cannot by definition fit into memory
2) Path to vector bin file: In order to create this file, I once again need Numpy array: 1)

In other words, this function defeats its own purpose since in order to use it, I need to put all my data that are not supposed to fit into memory... into memory...

I would suggest to make it accept an `Iterator[np.Array]` or correct the documentation.

Start at the build_disk_index entry point and its documentation; inspect how the current NumPy-array and vector-bin-path inputs are handled. Done means either iterator input is supported for large datasets or the documentation accurately describes the existing requirements, with relevant tests or documentation checks updated.

Written by the indexing model from the issue text.