Re-use cached state with the same version from any branch

[teor2345]

Motivation

In PR #4074, we check for unexpected state versions before running Google Cloud tests.

But we want tests to re-use the previous cached state with the same version.

Designs

We want to re-use the cached state from any branch, as long as:

• the state version is the same, and
• the state kind (checkpoint or tip) is the same.

If there is a state with that version on main, and on another branch, use the one from main.

If a cached state with that version can't be found, the state should be rebuilt.
(We currently check for changes to the state version constants.rs Rust file, but we should check for a matching cached state version instead.)

And then the tests should be run with that new state.

Out of Scope

Old cached state versions should be cleaned up:

• when the main branch has a higher state version.

I'm not sure what we should do if a previous cached state version has a bug. But we can make this decision later, because we only have one state version change planned, and it is a low priority.

As a workaround, we can change the state version in the code, which will regenerate a new cached state.

Related Work

• Old PRs can add a new "latest" cached state w/ the old state version #3881
• feat(ci): validate state version with cached state #4074

[ftm1000]

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