command: lift StdOut, StdErr into command, lift aggregator into output

[bobheadxi]

There doesn't seem to be a use case for changing StdOut, StdErr on-the-fly with Output, so we lift that configuration into Command, which greatly simplifies the initialisation of Output and reduces the amount of buffers we need to keep around. It also means that Output is almost purely about consuming output, which means aggregator is no longer needed, which also makes the story a lot simpler.

API-wise, the change looks like:

-  err = run.Cmd(ctx, "ls", "foobar").Run().StdOut().Stream(os.Stdout)
+  err = run.Cmd(ctx, "ls", "foobar").StdOut().Run().Stream(os.Stdout)

Closes #27

In the future, this could also improve the possibility of #5 by not having the full command be created immediately - instead we can export specifically the customizable components

[bobheadxi]

Current dependencies on/for this PR:

• main
  • PR command: lift StdOut, StdErr into command, lift aggregator into output #29 👈
    • PR output: add String() (string, error) #30

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[codecov-commenter]

Codecov Report

Merging #29 (b020a1b) into main (e4a6222) will increase coverage by 2.05%.
The diff coverage is 75.70%.

@@            Coverage Diff             @@
##             main      #29      +/-   ##
==========================================
+ Coverage   67.48%   69.54%   +2.05%     
==========================================
  Files           9        8       -1     
  Lines         366      348      -18     
==========================================
- Hits          247      242       -5     
+ Misses         96       85      -11     
+ Partials       23       21       -2     

Impacted Files	Coverage Δ
output.go	76.61% <74.86%> (-23.39%)	⬇️
command.go	60.00% <77.27%> (+23.63%)	⬆️
error.go	71.42% <100.00%> (ø)

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[bobheadxi]

I'm goiing to merge this directly because I have some exciting refactors coming