Add -w/--watch flag to test subcommand to watch for file changes

[brubsby]

Was tired of switching windows to test changes to my code. So I figured file watching a la rustlings would be of use.

Thought about having a whole new subcommand called watch that would test and then submit on passing, but this seemed better.

[clearloop]

hey @brubsby , thanks for the PR! could you please bump the version of the package btw, that I can update it in crates.io once merging this PR

[brubsby]

I've committed a version bump, let me know if it's sufficient! Though this morning I'm getting lots of:

[INFO  leetcode_cli::plugins::leetcode] Sending code to judge...
Anyhow(JSON error: expected value at line 1 column 1, please double check your session and csrf config.)

Though it seems to be happening regardless of -w or my changes. But my config still matches the browser values.

Edit: Looks like it was just a intermittent error that resolved itself before I could diagnose the exact problem.

[clearloop]

Edit: Looks like it was just a intermittent error that resolved itself before I could diagnose the exact problem.

This could be a network issue