fix(go): inherit template build users and release v0.1.4

[muxx]

Summary

• Omit the optional RUN user argument when it is empty, preserving the current build user for RunAs, NPMInstall, BunInstall, and GitClone.
• Add serialized-request regressions for default/configured users and explicit/global overrides, plus a KVM release smoke for user inheritance, npm installation, and Git cloning.
• Bump all SDK packages to 0.1.4 and regenerate the Go reference contract.

Validation

• Reproduced 14 failing cases before the fix; all regression cases pass afterward.
• Frozen dependency installs, format, lint, typecheck, JS/Python tests, and make go-check pass.
• Go statement coverage: core 90.6%, Code Interpreter 90.4%.
• Deterministic generation, release artifacts, and clean package-install checks pass.
• Full pre-release KVM smoke passes for JavaScript, Python sync/async, Go, Code Interpreter, CLI, and template builds.

This fixes the Go documentation live-run blocker found in SDK 0.1.3.