Fix and enable fuzzing

[AlekSi]

Refs #238.

[codecov]

Codecov Report

Merging #240 (0182bbd) into main (1eb6429) will increase coverage by 1.33%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #240      +/-   ##
==========================================
+ Coverage   48.67%   50.00%   +1.33%     
==========================================
  Files         108      108              
  Lines        5048     5051       +3     
==========================================
+ Hits         2457     2526      +69     
+ Misses       2172     2128      -44     
+ Partials      419      397      -22     

Impacted Files	Coverage Δ
internal/wire/op_msg.go	46.63% <100.00%> (+0.78%)	⬆️
internal/bson/document.go	44.33% <0.00%> (+0.97%)	⬆️
internal/fjson/fjson.go	85.52% <0.00%> (+3.94%)	⬆️
internal/fjson/document.go	50.00% <0.00%> (+4.16%)	⬆️
internal/fjson/double.go	72.91% <0.00%> (+6.25%)	⬆️
internal/bson/binary.go	46.80% <0.00%> (+6.38%)	⬆️
internal/bson/regex.go	45.65% <0.00%> (+6.52%)	⬆️
internal/fjson/array.go	60.86% <0.00%> (+6.52%)	⬆️
internal/bson/string.go	44.44% <0.00%> (+6.66%)	⬆️
internal/bson/datetime.go	51.35% <0.00%> (+8.10%)	⬆️
... and 12 more

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