add: run pre- and post- tasks

[metaist]

• add pre[-_]?{name} and post[-_]?{name} tasks
• add cli options: -s, --skip-prepost to skip both pre- and post-tasks

Later consider:

• options to skip just pre- or post-tasks (--skip-pre, --skip-post)
• whether to read this behavior from a project-specific or global configuration file

History
Lots of tools (npm, yarn, pnpm, pdm, etc.) look for task names that run before and after a particular task.

• node tools use pre{name} and post{name}
• python tools use pre_{name} and post_{name}
• tools have some way of skipping these types of tasks
  • some tools let you choose whether to skip just the pre-tasks or just the post-tasks (e.g., pdm

[metaist]

At first I was just going to implement this the way npm does. But on reflection, this actually contradicts the principle of visibility. npm does lifecycle things because it has all kinds of special situations in which it runs pre- and post-hooks.

Also package.json doesn't make it easy to have composite tasks so having pre- and post- hooks makes defining things a little easier.

We can be more explicit:

clean = "rm -rf build/"
pre-build = ["clean"]
build_wheel = "python -m build"
build = ["pre-build", "build_wheel"]

This way you can specify what needs to happen in what order exactly with minimal magic. I'll revisit this in the future if it seems necessary.

[metaist]

My thoughts on this have changed. Going to add --pre and --post args as experimental.