better handle error state during command edit

[daretodave]

steps to repo:

• open editor for command file

:cmd

-add an error to the typescript (e.g invalid character, or misspell void/async)

• save

mterm will indicate "commands saved" but it could not reload due to the error. you can see this is you look at the yarn dev output

todo:

• wrap :cmd logic with a try/catch and display error in a way that the user can see it
• see if :settings edit has the same issue maybe?
  • run :settings edit
  • see if adding a bogus json character etc will say "settings saved"