Feature request: Implement a --run option

[mhheise]

Hi! 👋 Thank you for building siroc.

I have been experimenting with siroc and it has been quite easy to implement. The only use case that I have encountered so far that hasn't been supported "out-of-the-box" is running the resulting bundles through Node once built. I have been able to use @rollup/plugin-run in the rollup options do this, but I wonder if this is something that you would like to support via the library via some sort of --run option. This is something that I saw in my research of esbuild-based tools like estrella and esmon.

Ideally, I would be able to:

• Use siroc build --run to build and run a package once;
• Use siroc build --watch --run to build and run a package that reloads on changes; and,
• Pass through options to the underlying @rollup/plugin-run (like the execArgv option in @rollup/plugin-run allows).

Of course, if you decide not to take this on, no worries -- the existing experience already works well for me!

Thanks!