feat: change field names to snake case

[frostming]

Summary

Change the field names for models to be snake case

Constructing the models should be backward-compatible, but accessing is not:

req = InitializeRequest(protocolVersion=1)  # valid
req = InitializeRequest(protocol_version=1)  # valid
req.protocolVersion  # AttributeError
req.protocol_version  # valid

So this should be considered a breaking change, should better open a dedicated branch and merge to it.

Checklist

• Conventional Commit title (e.g. feat:, fix:).
• Tests cover the change or are not required (explain above).
• Docs/examples updated when behaviour is user-facing.
• Schema regenerations (make gen-all) are called out if applicable.

[PsiACE]

LGTM 💯

It's great to have a true Python expert helping us with this.

Just a heads-up: I've prepared a branch named 0.7.x as the target branch. I plan to introduce these significant pythonic changes in the next protocol version release.