chore: simplify decoder's bits

[muktihari]

• Now we only check whether bits' store has reach zero. The bits validity checking is removed since we already check the value validity in decoder and The bitsize checking is also removed since it's not FIT files related but it's an implementation detail of Profile.xlsx.
• The zero size of bits is now reserved as global variable, this makes comparing bits to its zero value a bit faster.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (fa631b9) to head (68bab50).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #488   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           42        42           
  Lines         3853      3855    +2     
=========================================
+ Hits          3853      3855    +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.