Add tests for internal type definitions in TableauExpansionTypes

[rizumita]

Description

The TableauExpansionTypes.swift defines important internal types used in the model checking algorithms, but has no test coverage. While these are internal types, they should be tested indirectly through their usage.

Tasks

• Create integration tests that exercise FormulaAutomatonState usage
• Test BuchiAlphabetSymbol with different PropositionIDType implementations
• Test ProductBATState creation and equality
• Verify hashability of ProductBATState
• Test these types through the algorithms that use them

Priority

Low - These are internal types that can be tested through their usage in other components.

Location

Sources/TemporalKit/ModelChecking/Algorithms/TableauExpansionTypes.swift

Note

Since these are internal types, they should be tested indirectly through the public APIs that use them, rather than exposing them for direct testing.