Restructure package for domain-driven design

Reorganise package structure to improve separation of concerns:
- instruments/ - SCPI, transport, drivers, interfaces, factory
- simulation/ - physics engine, virtual instruments, server
- framework/ - test runner, logger, limits, context
- tests/ - thermal/, electrical/ (DVT test implementations)
- data/ - repository, models
- reporting/ - generator, templates
- app/ - CLI, config, dashboard

This structure enables:
- Reusable instruments package for other test suites
- Clear separation of simulation (dev) vs production code
- Domain-focused package organisation

Updated documentation to reflect new paths.

src/py_dvt_ate/tests/__init__.py

@@ -1 +1,6 @@
-"""DVT test implementations."""
+"""DVT test implementations.
+
+Contains characterisation test suites organised by category:
+- thermal/ - Temperature-related tests (TempCo, etc.)
+- electrical/ - Electrical tests (load regulation, etc.)
+"""