Shard the `test` suite in CI

https://github.com/clockworklabs/SpacetimeDB/pull/5705 sharded the smoketests using nextest. We'd like to do something similar for the rust test suite. This is the job that runs cargo test with some exclusions.

Currently this job is the most expensive CI job at around 30 minutes. Our goal is to have individual jobs be bounded at around 5 minutes. Definitely no more than 10 minutes.

One of the biggest parts of the overall test suite is the sdk test suite. As a first step it would probably be useful to split that out into its own job. In principle, it should be very similar to the smoketests.

For reference, smoketest modules are compiled ahead-of-time in their own separate Smoketests Build job. Each individual shard downloads their build artifacts which include the cli, standalone, and the pre-built WASM modules. Each shard then executes each individual smoketest by starting spacetimedb in its own process, publishing the appropriate module, and executing the test. I think we should use the same pattern for the sdk tests too.