Add retriable/transient exceptions

[ryannedolan]

Summary

• Throw SQLNonTransientException (or derivative) for validation errors, etc.
• Throw SQLTransientConnectionException for IO errors encountered when loading the catalog, etc.

Details

Calcite frequently uses unchecked exceptions, and Hoptimator follows that pattern where necessary. Unfortunately, this means client code often receives opaque RuntimeExceptions. Where possible, we want to instead throw SQL[Non]TransientException, s.t. client code can decide whether to retry or surface an error to users.

Testing

None. Client code will be tested externally.

N.B. we don't expect 100% coverage wrt this transient-vs-non-transient distinction at this point. As future RuntimeExceptions are encountered, we may need to revisit this problem.

[jogrogan]

Nice!