BUG/MAINT: Correct uinteger buffering in SFMT and dSFMT

[bashtage]

Remove unused buffers from dSFMT
Add to reset in SFMT
Add test for these

[pep8speaks]

Hello @bashtage! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file randomgen/tests/test_direct.py:

Line 369:21: E231 missing whitespace after ','
Line 375:30: E231 missing whitespace after ','
Line 384:21: E231 missing whitespace after ','
Line 391:37: E231 missing whitespace after ','

[codecov]

Codecov Report

Merging #161 into master will increase coverage by 0.2%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master     #161     +/-   ##
=========================================
+ Coverage   95.16%   95.36%   +0.2%     
=========================================
  Files          33       34      +1     
  Lines        9155     9706    +551     
  Branches      134      152     +18     
=========================================
+ Hits         8712     9256    +544     
- Misses        421      427      +6     
- Partials       22       23      +1

Impacted Files	Coverage Δ
randomgen/dsfmt.pyx	92.78% <ø> (-2.07%)	⬇️
randomgen/tests/test_direct.py	99.27% <100%> (+0.05%)	⬆️
randomgen/sfmt.pyx	94.17% <100%> (+1.1%)	⬆️
randomgen/hc128.pyx	94.2% <0%> (ø)
randomgen/aes.pyx	90.07% <0%> (+0.16%)	⬆️
randomgen/tests/test_smoke.py	98.66% <0%> (+0.21%)	⬆️
randomgen/mt19937.pyx	92.85% <0%> (+0.35%)	⬆️
... and 3 more

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