ci: evaluate one-job Windows test workers

[kmbroai]

Summary

• keep one unsharded Windows check and one Test step
• run all Windows test files through four long-lived Bun workers while each worker stays serial
• leave Linux/macOS and release test commands unchanged

Measured result

• Windows node-22 Test: 154s; 934 pass, 53 skip, 0 fail; 987 tests across 41 files
• Windows node-24 Test: 169s
• Ubuntu node-22 Test: 69s
• Ubuntu node-24 Test: 65s
• This preserves coverage and roughly halves Windows test time, but does not reach Ubuntu parity on one Windows runner.

Testing

• pnpm --dir sdk/typescript run types
• pnpm --dir sdk/typescript run format
• bun test --timeout 30000 ./sdk/typescript/tests-ts/skeleton.test.ts
• local grouped-worker smoke across all 41 test files