Improve the performance in cast kernel using AsPrimitive trait in generic dispatch

[sundy-li]

Beat arrow2 cast performance less than 10 LOC, about 7 times faster in casting 2^20 size u32array to u64array.

Benchmark codes:

https://github.com/sundy-li/learn/blob/master/arrow-vs-arrow2/benches/cast_kernels.rs

Gnuplot not found, using plotters backend
cast u32 to u64 1048576 time:   [4.3537 ms 4.3615 ms 4.3702 ms]                                     
                        change: [-0.0612% +0.1772% +0.4521%] (p = 0.17 > 0.05)
                        No change in performance detected.


cast u32 to u64 v2 1048576                                                                            
                        time:   [630.99 us 645.11 us 664.46 us]
                        change: [-11.727% -4.8932% +1.8462%] (p = 0.20 > 0.05)
                        No change in performance detected.