[choreo] Document Updater

[oh-yes-0-fps]

Needs unit tests but has been tested on my robot project

This pr also adds trackwidth to .traj output field to show off the upgrader, its just a dummy value of 1.0 for now

Fixes #570.

[calcmogul]

What are the steps for adding another schema version upgrade? We should document whatever that is in the interest of documenting maintenance tasks.

[oh-yes-0-fps]

What are the steps for adding another schema version upgrade?

Incrementing the constants for the schema version (its just an incrementing integer now for simplicity idk how you define semver for the schema stuff when any change is "breaking").
Add a new upgrader action in upgraders.rs for the changes you made
Update the choreolib code if its needed.

I admit there is more that goes into it than i would like but most actions that reduce complexity in schema management add complexity to some build step.

[shueja]

Architecturally this seems reasonable. I'll have to think about ramifications of changing save file versioning to an int. I also don't know if we should require that Choreolib changes matching spec changes must go in the same PR.

[spacey-sooty]

I also don't know if we should require that Choreolib changes matching spec changes must go in the same PR.

I think we risk creating issues/having Choreolib fall behind similar to how C++ does if it's not updated in the same PR.

[shueja]

I agree. I'm just wondering what effect that will have on PRs getting carried through to mergeability.

[calcmogul]

If we can't get it done in the PR itself, I'd be concerned about it ever getting done, since maintainers can push directly to PRs.

[calcmogul]

Items to address:

• What is the "trackwidth" field in the .traj when it's a swerve trajectory Removed for this PR.
• ChoreoLib C++/Java/Python changes to use an int for version number
• Make ChoreoLib C++/Java/Python JSON load fail non-fatally if version is a string
• Unit tests for the already implemented upgrader, and a clear place to put more

Item 3 is somewhat related to another issue about assembling a common set of test JSONs for all sorts of tests.

OBE

[shueja]

Trackwidth work moved to #969