Enforce code formatting with ruff format (#45)

[janhoy]

First commit in this PR branch

• Enable ruff format --check . in the make lint target (was commented out)
• Add make format target as the canonical way to auto-format sources
• Document make format / make lint workflow in DEVELOPER_GUIDE.md and AGENTS.md

Second commit

• Result of ruff format . - reformats all source files

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[epugh]

Dunno... Do we use ruff format for other python code across Solr project? Does all of this reformatting ever prevent us from updating solr-orbit with innovations form any of it's upstream projects? Though we have renamed so much.. and AI tooling of course may make that less important....

[janhoy]

Dunno... Do we use ruff format for other python code across Solr project?

Well, this is our largest python codebase, so I think it matters more than for the utility scripts we have in main repo.

We could surely maintain this tool with just loosely documented conventions, but I think we have good experience with code formatting both for java and go (operator).

If we do this, we should add a .git-blame-ignore-revs file with the commit sha of the reformatting, so git bisect won't get confused.