[unit-test] Add comprehensive boolean expression tests with 32 test cases

- Create boolean_expression_tests module in expression_eval.rs
- Cover all boolean operators: AND, OR, NOT with truth table tests
- Test basic operations: all combinations of True/False for AND/OR
- Test NOT operator with both True and False inputs
- Add variable integration tests with boolean values
- Test nested boolean expressions and operator precedence
- Include complex expressions combining boolean, relational, and arithmetic
- Test De Morgan's law equivalence verification
- Add edge cases: double negation, chained operators
- Test integration with relational operators (>, <, ==, etc.)
- Include error handling for invalid types (integers, strings, reals)
- Test undefined variable handling in boolean contexts
- Verify proper evaluation order in mixed expressions
- Add comprehensive operator chaining tests
- Maintain consistent test organization alongside existing modules

Author: rbonifacio