feature request: add automatic opening exercise file when verify fails

[ohk990102]

It is inconvenient to open every new exercise on editor.
Automatic opening exercise file will be convenient to some people who use visual editor (i.e., vscode) for solving rustlings.

https://github.com/ohk990102/rustlings/blob/7097f0c8df17adf91f60600aa6df24e990efdc1d/src/verify.rs#L235-L239

This is poc, and it works well on vscode.

[manyinsects]

This is not applicable to people using other editors, though. If using the proper command to open files (e.g. xdg-open on Linux), and if it was cross-platform, I wouldn't object to merging this (provided it's behind a command-line flag for watch, as I think enabling this by default is counter-intuitive).

[mo8it]

Closing because opening a file in an editor while still seeing Rustlings in the background is not possible with terminal editors like Helix (which I use).

You can use a shortcut like CTRL+p in VSCode to quickly open a file instead of using the file tree.