cmd: Merge decode/encode into a single cobs command

[pdgendt]

Use subcommands for decode and encode, the main command is 'cobs'.

[codecov]

Codecov Report

❌ Patch coverage is 96.34146% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.46%. Comparing base (b1c3a84) to head (e81b7cf).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/cobs/main.go	96.34%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #36      +/-   ##
==========================================
- Coverage   98.26%   97.46%   -0.80%     
==========================================
  Files           1        2       +1     
  Lines         115      197      +82     
==========================================
+ Hits          113      192      +79     
- Misses          1        4       +3     
  Partials        1        1              

Files with missing lines	Coverage Δ
cmd/cobs/main.go	96.34% <96.34%> (ø)

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Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

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