test: add class-level contract tests for ConditionGroup, PropertySet, FeatureFlag, and transform attributes

[HeyItsGilbert]

Summary

The class layer has no contract tests. Several methods are broken (AddProperty, IsValid) and several transform attributes have dead code paths (ConditionGroupTransformAttribute.FromJson). Tests at this layer would have caught those bugs and will prevent regression after they're fixed.

New File(s)

tests/Classes.tests.ps1 (or split into ConditionGroup.tests.ps1, PropertySet.tests.ps1)

Tests to Add

ConditionGroup constructor

• Each pair of {AllOf+AnyOf, AllOf+Not, AnyOf+Not} throws (after fix for fix(ConditionGroup): constructor allows two simultaneous group operators — silent logic bypass #13)
• Property without Operator/Value throws
• Group + flat fields (AllOf + Property) throws

ConditionGroup methods

• IsValid() returns $true for a flat leaf condition
• IsValid() returns $false for a partial condition (missing Value)
• ToString() for each shape: flat, AllOf, AnyOf, Not, nested

ConditionGroupTransformAttribute

• Hashtable input → ConditionGroup
• ConditionGroup input → passthrough
• String input (after FromJson is added, issue fix(ConditionGroupTransformAttribute): Transform calls [ConditionGroup]::FromJson() which doesn't exist #12) → ConditionGroup
• Unsupported type → throws useful message

PropertySet

• AddProperty adds entry keyed by Name (after fix for fix(PropertySet): AddProperty throws on every call — wrong hashtable.Add signature #11)
• AddProperty returns $this for chaining
• GetProperty returns the correct PropertyDefinition
• ContainsKey returns true/false correctly
• FromFile sets Name correctly (after fix for fix(PropertySet): FromFile silently sets Name to $null — .BaseName on a string #14)
• Save → FromFile round-trip preserves all properties and validation constraints

PropertyDefinition.Validate

• Returns $true when value is valid
• Returns $false (and emits warning) for each constraint violation
• Returns $true when no validation is configured

FeatureFlag

• FromJson round-trips correctly
• FromFile round-trips correctly
• Save writes valid JSON that re-parses to equivalent object

Notes

• Depends on: fix(PropertySet): AddProperty throws on every call — wrong hashtable.Add signature #11 (AddProperty fix), fix(ConditionGroupTransformAttribute): Transform calls [ConditionGroup]::FromJson() which doesn't exist #12 (ConditionGroupTransformAttribute fix), fix(PropertySet): FromFile silently sets Name to $null — .BaseName on a string #14 (FromFile Name fix)
• Found by Sage Nakamura, Jordan B., and Glenn