diff: Derivative Performance

Created by: SellJamHere

Fixes #380 (closed)

The PR removes the concurrent code path in the Derivative function. To maintain backwards compatibility, the concurrent value in Settings is unchanged. However, the setting is now a no-op.

benchstat comparison of the Derivative pre/post PR:

# benchstat old.txt new.txt 
name                       old time/op  new time/op  delta
DerivativeSerial-8         67.0ns ± 0%  28.3ns ± 0%   ~     (p=1.000 n=1+1)
DerivativeConcurrent-8     1.98µs ± 0%  0.03µs ± 0%   ~     (p=1.000 n=1+1)
Derivative2ndSerial-8       116ns ± 0%    74ns ± 0%   ~     (p=1.000 n=1+1)
Derivative2ndConcurrent-8  2.88µs ± 0%  0.07µs ± 0%   ~     (p=1.000 n=1+1)