sql: add randomized testing for gist decoding

[rytaft]

Is your feature request related to a problem? Please describe.
We have found that there are cases where decoding a gist can cause panics when the encoded format doesn't exactly match what is expected by the code. For example, see #113900. This is especially likely when decoding a gist that was encoded by a different version of CockroachDB.

The DB console performs gist decoding of sampled queries, making it likely that a customer might run into this issue in production.

Describe the solution you'd like
We'd like to discover cases where gist decoding can cause panics so they can be fixed before customers run into them in production. One idea is to randomly generate queries using sqlsmith, encode them as a gist, and then make sure they can be decoded without a panic. We could also write this as a mixed version roach test.

Jira issue: CRDB-35283

[mgartner]

@yuzefovich are you still planning on doing this during 24.1 stability, or should we push to the backlog or 24.2?

[yuzefovich]

I still plan to do it during the stability period.