Align test-layout guidance with grouped public command tests

[MariusStorhaug]

The current module standards text states: "One test file per public command for unit tests; integration tests grouped by scenario."

This conflicts with the intended model used in Domeneshop, where unit tests are grouped per public command group (feature/domain) rather than per command file.

Request

Update the testing/layout guidance to support and prefer one test file per public command group (for grouped public commands), while still allowing root-level test files for ungrouped commands and cross-cutting coverage.

Reference

• Implementation example: 🌟[Major]: Domeneshop API capabilities now available Domeneshop#16
• Commit with grouped test layout: PSModule/Domeneshop@fe18c35