Splitting sdk-test out of Test Suite

[JasonAtClockwork]

Description of Changes

First step to #5839 splitting out the SDK tests and partition:

• Added cargo ci sdk-tests command for local SDK test execution
• Split Rust SDK tests out of the main Test Suite job
• Added a build job that precompiles SDK modules and prepares reusable client artifacts
• Created separate native and browser nextest archives and client artifacts
• Sharded native and browser SDK tests into two partitions each

API and ABI breaking changes

No breaking changes - only tests

Rollback safety impact

n/a

Expected complexity level and risk

2 - Splitting up requires CI work and mucking with test setup for preparing clients

Testing

• Manual test of each partition
• Full local run of sdk-test to confirm no major issues
• Utilizing CI to fully test

[joshua-spacetime]

This job currently takes 13m in the latest CI run. I believe that's probably because of the current spacetimedb-testing dependency which compiles most of standalone.

Ideally we'd like to be able to just download and use the CLI and standalone binaries that are produced by the "Upload build artifacts" job.

I haven't looked into which parts of spacetimedb-testing the sdk test suite is using and how hard it would be to remove this dependency, but that's probably worth looking into. Alternatively we could wait for CI runner image cache which should reduce this build time significantly.