chore: make fields/developerFields n buffer size 255 instead of 256

[muktihari]

A byte value is between 0-255, so field's num, n Fields and field's value size max value is 255. The same logic applies for developer fields as well. So we only need 255 size for those values such as when creating fieldsArray in decoder, fields' pool in mesgdef, etc. Even the maximum number of character in a string should not exceed 255.

And for factory, we keep the fields' size 256 as we want to ensure O(1) field lookup, and technically, field number 255 is still a valid byte even if it's an invalid field number.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (6836dae) to head (5a14556).

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #303   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           42        42           
  Lines         3691      3691           
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  Hits          3691      3691           

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