Make unsafe_load-based transmutes GC-protected

[pthariensflame]

Fixes #29.

[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.18%. Comparing base (bff009e) to head (6a59a70).
⚠️ Report is 17 commits behind head on master.

Files with missing lines	Patch %	Lines
src/arm/aesni_common.jl	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master      #31       +/-   ##
===========================================
+ Coverage   79.26%   98.18%   +18.91%     
===========================================
  Files          10        9        -1     
  Lines        1095     1101        +6     
===========================================
+ Hits          868     1081      +213     
+ Misses        227       20      -207     

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[sunoru]

LGTM. Thank you so much for doing this.