LazyIndex

[urigoren]

Added a LazyIndex class with the same API as Index.
Useful when having multiple indices with lazy initialization.

This also fixes the super annoying bug that crashes hnswlib (without an exception) if calling add_items or get_max_elements before calling init_index.

This PR in its first version probably needs some work, I'd love to hear your feedback, thanks :-)

[yurymalkov]

Hi @urigoren ,
Thanks!

One thing I would change is the name of the file, since it directly collides with hnswlib name, which might cause ambiguity if imported within the folder.
Another thing is - adding a short description in the file will be helpful for others to understand its purpose.

[urigoren]

Hi, @yurymalkov - done.
Could you please review ?

Thanks!

[yurymalkov]

Looks good to me. Thanks!