benchmarks: add benchmark for Stream

[robfig]

No description provided.

[codecov]

Codecov Report

Merging #439 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #439      +/-   ##
==========================================
- Coverage   86.46%   86.42%   -0.04%     
==========================================
  Files          41       41              
  Lines        5106     5106              
==========================================
- Hits         4415     4413       -2     
- Misses        555      557       +2     
  Partials      136      136

Impacted Files	Coverage Δ
reflect_struct_decoder.go	81.09% <0%> (-0.27%)	⬇️

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[robfig]

There is no benchmark covering Stream operation, where I believe I found a performance bug. This commit adds a benchmark in preparation for a patch to fix #438