test: shuffle unit test order

[emil14]

Summary

• run the existing non-e2e unit suite with Go test shuffle enabled
• keep local Makefile and GitHub Actions invocation identical
• document that the emitted shuffle seed reproduces order-dependent failures

Validation

• make test-unit
• repeated full unit runs with race and distinct shuffle seeds
• pre-commit: gofix
• pre-push: gofix-check, golangci-lint (0 issues)