chore: use split common modules

[JustinBeckwith]

Next step is to remove common

[codecov]

Codecov Report

Merging #200 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #200   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           9      9           
  Lines         892    900    +8     
=====================================
+ Hits          892    900    +8

Impacted Files	Coverage Δ
src/subscription.js	100% <100%> (ø)	⬆️
src/topic.js	100% <100%> (ø)	⬆️
src/iam.js	100% <100%> (ø)	⬆️
src/subscriber.js	100% <100%> (ø)	⬆️
src/index.js	100% <100%> (ø)	⬆️
src/connection-pool.js	100% <100%> (ø)	⬆️
src/snapshot.js	100% <100%> (ø)	⬆️
src/publisher.js	100% <100%> (ø)	⬆️

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