[FEA]Vamana API Disk Index Support

Is your feature request related to a problem? Please describe.
The Vamana python api currently only supports getting loaded by StaticMemoryIndex of diskannpy,
need the Vamana api exposed via python to support exporting the index in a way that can be used by the StaticDiskIndex class in diskannpy (https://microsoft.github.io/DiskANN/docs/python/latest/diskannpy.html#StaticDiskIndex).
We need this to be able to allow customers to use the disk index so that they can support very large indexes that might not fit on resource (cpu/gpu). So we want to allow them to use it from disk, even if search might be slower.

Describe the solution you'd like
I'd like to see the saving of the vamana graph in cuvs work with the vectors_from_file (https://microsoft.github.io/DiskANN/docs/python/latest/diskannpy.html#vectors_from_file), so that I can then create the appropriate StaticDiskIndex.

Start by reading the Vamana Python API and comparing its current StaticMemoryIndex loading path with diskannpy's StaticDiskIndex and vectors_from_file requirements. Confirm what exported graph and vector data those entry points accept; done means a cuVS-saved Vamana index can be loaded and used through StaticDiskIndex.