Made the golang 'version' package internal

[cmaglie]

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• Tests for the changes have been added (for bug fixes / features)
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What kind of change does this PR introduce?

It makes the version package internal.

What is the current behavior?

The package version is publicly importable.

What is the new behavior?

The package version is private.

Does this PR introduce a breaking change, and is titled accordingly?

Strictly speaking, yes. By the way, this is a purely theoretical breaking change because the version package is useless outside the Arduino CLI, and there is no point in exporting it. I'll consider this patch more of a bug fix than a breaking change.

Other information

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.52%. Comparing base (a9597d6) to head (865216e).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2767      +/-   ##
==========================================
- Coverage   67.54%   67.52%   -0.02%     
==========================================
  Files         237      237              
  Lines       22362    22362              
==========================================
- Hits        15104    15101       -3     
- Misses       6066     6068       +2     
- Partials     1192     1193       +1     

Flag	Coverage Δ
unit	67.52% <ø> (-0.02%)	⬇️

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