internal: adopt Turborepo task orchestration

[samohovets]

Summary

• replace serialized root workspace commands with a dependency-aware Turborepo task graph
• add package-level build, typecheck, test, lint, and formatting tasks where applicable
• cache Studio and native build outputs with pinned Node and Rust toolchain inputs
• configure the SHA-pinned GitHub Actions Turborepo cache service

Closes #2.

Changelog

Public summary:

• None.

Context:

• Internal build and validation tasks now run in parallel where safe and can restore generated Studio and native artifacts from cache.

Verification

• pnpm fmt
• pnpm validate
• Deleted packages/studio/dist and the generated native .node file, then ran pnpm build and confirmed both outputs were restored from the local Turbo cache.