speedup jitter_run

[segasai]

Jitter_run is slow. (it takes 60% of time of test_dyn.py)

The patch makes trivial speedups

Before (cProfile on test_dyn.py)

    ncalls  tottime  percall  cumtime  percall filename:lineno(function)
     1664   79.624    0.048   97.583    0.059 utils.py:380(jitter_run)

After

     1664   69.921    0.042   77.390    0.047 utils.py:380(jitter_run)

[coveralls]

Pull Request Test Coverage Report for Build 864998055

• 13 of 13 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.04%) to 72.003%

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Totals
Change from base Build 861576137:	-0.04%
Covered Lines:	3364
Relevant Lines:	4672

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💛 - Coveralls