test: add more tests, remove test attrs on prod build.

[morganney]

• Adds test to collect more coverage.
• Only significant change to source code was having the controllers underling play method become async to account for it handling playing of HTMLAudioElement.play which is itself async, i.e. promise returning. No public facing API has changed to become async, however.

[codecov-commenter]

Codecov Report

Merging #20 (b3fc3ff) into main (1026b7b) will increase coverage by 21.40%. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##             main      #20       +/-   ##
===========================================
+ Coverage   75.47%   96.88%   +21.40%     
===========================================
  Files           7        7               
  Lines         477      481        +4     
  Branches      131      133        +2     
===========================================
+ Hits          360      466      +106     
+ Misses        117       15      -102     

Impacted Files	Coverage Δ
src/icons.tsx	100.00% <ø> (ø)
src/component.tsx	100.00% <100.00%> (+13.04%)	:arrow_up:
src/control.tsx	100.00% <100.00%> (+11.76%)	:arrow_up:
src/controller.ts	98.03% <100.00%> (+38.33%)	:arrow_up:
src/hook.tsx	93.60% <100.00%> (+8.98%)	:arrow_up:
src/highlighter.tsx	100.00% <0.00%> (+10.00%)	:arrow_up:

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