add `bacon.toml` for easier new dev experience

[PatrickLaflamme]

Proposal to use Bacon to make the standard operations of running the specification tests a little simpler during development.

How to use:

1. install bacon with cargo install --locked bacon
2. press 1 to run only the specification.md tests once.
3. press 2 to run only the staging.md tests once.
4. press 3 to run all tests once.
5. press 4 to run only the specification.md tests and watch for changes.
6. press 5 to run only the staging.md tests and watch for changes.
7. press 6 to run all tests and watch for changes.

Bacon will watch for changes in the source sets and re-run the tests on change. This can help optimize the feedback cycle and accelerate development.

[kaleidawave]

Awesome, just looked into Bacon. Looks like it solves a problem of unifying the current jumble of scripts this project uses.

Few questions before I merge

• Could you add a short overview of how to use it (similar to the PR body) to CONTRIBUTING.md under a heading like ### Bacon (script runner)?
• I would quite like to use this, but are a little bit unsure of the watch mode (as similar watch tools that run compilation lots kill my laptop battery). Does it run ALL the scripts in the background or just the one selected? Is there a non-watch mode?

Other than that looks great, thanks for introducing me to it (hadn't heard of it before). Also might add some more scripts that I use to it later.

[PatrickLaflamme]

added some details in the CONTRIBUTING.md file. Also created some jobs that don't watch for changes. If you want to re-run, just press the hotkey to trigger a run again.

I find it particularly useful in my IDE to have a terminal open running the spec tests, and then as I make changes I can see how my changes affect the test outcomes. Makes iterations SUPER fast.

[kaleidawave]

Thanks for adding documentation to contributing. Excited to try this!