Various crush run improvements

[meowgorithm]

This is a series of small-ish improvements to crush run. The main things are:

• There were extra newlines printing above the output. Now they're gone.
• There was no newline printing at the end of the output, which meant the prompt would print over the output after exit. That is fixed.

Other things to do in another pass:

• Run the spinner on stderr
• Make this work with pipes when output is not stdout and input is a pipe, i.e.
  • crush run "What is this?" <<< main.go > output.txt
  • curl https://charm.land | crush run "What is this?" > output.txt

[andreynering]

Seems solid!

As a little extra thing, if you want to take a look while you're at it: the Generating... text is a little hard to read when using the terminal light mode.

[andreynering]

Does this cause the some bugs on iTerm2/SSH that #1329 fixed for interactive?

If so, we might want to address them.

/cc @aymanbagabas

[meowgorithm]

Fwiw this was a present prior to this PR and lives in many places around the codebase.

[meowgorithm]

Seems solid!

As a little extra thing, if you want to take a look while you're at it: the Generating... text is a little hard to read when using the terminal light mode.

Oh wow, I didn't realize that was hard-coded to light grey; will fix prior to merging. Thanks for the detailed review!

[meowgorithm]

Alright, fixed for you @andreynering.

[andreynering]

Looks great!