Add multi-arch builds to CI/CD. Fix 32bit builds.

[landhb]

Fixes #8

[codecov-commenter]

Codecov Report

Merging #9 (a005074) into main (f145269) will increase coverage by 0.02%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main       #9      +/-   ##
==========================================
+ Coverage   78.31%   78.33%   +0.02%     
==========================================
  Files           8        8              
  Lines         415      420       +5     
==========================================
+ Hits          325      329       +4     
- Misses         90       91       +1     

Impacted Files	Coverage Δ
src/ffi/functions.rs	88.23% <100.00%> (ø)
src/ffi/types.rs	68.18% <100.00%> (+3.18%)	⬆️
src/key.rs	72.11% <100.00%> (-0.17%)	⬇️
src/keyring.rs	81.00% <100.00%> (-1.00%)	⬇️
src/metadata.rs	100.00% <0.00%> (+2.56%)	⬆️

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