Format with air

[hfrick]

closes #168

This does a few things:

• set up the standard configuration of air: this basically turns on air when working in Positron/VSCode
• add 2 GHA: one checks that the code is formatted according to air's rules, the other one opens code suggestions on a PR to align the formatting (if necessary). The second one allows contributors to use air formatting, even when they don't have air installed/set up.
• tweaks air's config for spatialsample: the template for vcts is currently exempt
• finally: run air over the whole thing

Does that work for you? What's your IDE these days?

[hfrick]

Haha, failing the air action in the "let's use air" PR 😂 My air version locally is behind the GHA one! Lemme fix that

[hfrick]

The failing test-coverage action is fixed in #173.