Add check_rerun_command util to commands.py

[TizzySaurus]

Rewrites the logic of the eval command in python-discord/bot to create a re-run util (the eval command implementation had flaws, e.g including the python version to run in the edited message caused it to break since the version would be treated as code, and not the python version argument).

The core idea:

• User invokes a command that calls the check_rerun_command util.
  • If the passed context's message content is edited within REDO_TIMEOUT seconds, and the user then reacts with the 🔁 emoji that appears within 10 seconds, then the util will rerun the command (NB: this means commands with usage statistics will have the rerun add to the statistic, which doesn't currently happen but we arguably want this anyway).
  • Otherwise, the appropriate error message will appear, and the user won't be able to edit and re-invoke anymore.

This is made since python-discord/sir-lancebot#1062 asks for re-run, and as such I got approval from @mbaruh in the staff-lounge to move (and as it turns out, fix) the code from bot.

I have thoroughly tested this but there's of course still a chance I missed something. Example usage of the util to aid with testing:

@bot.command()
async def greet(ctx, *, name: str = "World"):
    response = await ctx.send(f"Hello, {name}!")
    await check_rerun_command(ctx, response)

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