Fixed compatibility with numba v0.51.2

[ashrielbrian]

This fixes the deprecation warnings from numba (#3 ) due to object mode fallback when nopython mode fails.

1. Redundant @jit decorators were removed.

• These were decorators that did not speed up the code due to numba object mode fallback.

2. Added explicit nopython decorators: @njit

• that way, if there is a compile failure, an error will be explicitly thrown.

3. Refactored functions to be numba-compatible.

• np.int -> np.int_
• np.bool -> np.bool_
• np.average -> np.mean
• refactored the loop get_minimum_seam into a separate function and added the @njit decorator.

These refactorings did not have any noticeable effect on the performance of the algorithm during benchmarking.