v0.9.0

What's Changed

• chore(dev→main): routine PR cadence for CodeRabbit review by @Snider in #2
• v0.9.0 compliance: full upgrade against core/go reference by @Snider in #3
• restructure to /go/ subtree (Phase 1, Mantis #1231) by @Snider in #4
• Refresh submodules, add EUPL-1.2 license, and fix build issues by @Snider in #5

Full Changelog: v0.2.2...v0.9.0