QoL changes to launching server and other fixes

[ml-evs]

• Allow config to be passed programmatically
• Use new optimade-python-tools option for creating indices by default
• Better warnings on initial JSONL ingestion
• Add upper Python version pin to 3.13, as pymatgen does not support it (but they accidentally released a PyPI version that said they did, so things don't quite work as they're meant to)
• Remove pybtex: we never added any code that uses this, and pybtex is now very out of date (and leads to errors for packaging).
• Added a CODEOWNERS file
• Allow the user to override the underlying OPTIMADE server config by using OPTIMAKE_ prefixed env vars
• Fix coverage in CI

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[eimrek]

Thanks Matthew, looks great, but will give test it out next week.

[ml-evs]

Thanks Matthew, looks great, but will give test it out next week.

Thanks, no rush! I'm using this "in production" elsewhere but feel free to make any fixes you see fit

[ml-evs]

I ended up overloading this PR with all the bits I needed, but the commits should be thematic and can be reviewed one at a time

[ml-evs]

This might be the one bit that is problematic @eimrek -- I added the ability to create a unique ID index to optimade-python-tools which is currently unreleased, when it gets released, serve will start making a unique index by default, which may conflict with any existing indexes you have... We could always set this to false by default to keep the old behaviour, and user's can now pass it as an env var anyway.