feat: add DeploymentPolicy validation and defaults with tests

[t0mmylam]

Add Comprehensive DeploymentPolicy Validation Tests

What

Adds comprehensive unit tests for DeploymentPolicy validation and defaulting logic, covering all requirements for strategy validation, budget constraints, compartment rules, and default inheritance.

Why

• Ensures robust validation of deployment policies before they're applied
• Prevents configuration errors that could impact rollout safety
• Provides comprehensive test coverage for complex policy validation logic

Changes

• Strategy validation: Ensures exactly one strategy type (fixed/linear/exponential) is set
• Bounds validation: Tests all numeric constraints for strategy parameters
• Budget XOR validation: Enforces percent/count mutual exclusivity
• Compartment validation: Unique names and non-duplicate selectors
• Default inheritance: Compartments inherit strategy from policy default
• Code refactoring: Eliminated duplication with helper functions