Rewrite part of library in Cython

[R1j1t]

At present the time-spent on 1 sentence is around ~0.7sec for spaCy small models on CPU. With the assumption that Cython can bring down the compute time.

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[R1j1t]

Reopening with the hope that, I will work on this

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.