Add owned Vulkan command API

[antono3]

Summary

• add owned command pools tied to the logical device queue family
• add primary command-buffer allocation, explicit free/reset/begin/end helpers, and raw handles
• document pool/device lifetime rules and extend ergonomic API tests

Local checks

• v fmt -verify ergonomic/ergonomic.v ergonomic/ergonomic_test.v
• v -check-syntax ergonomic
• git diff --check

Full compilation is delegated to GitHub Actions.