JsonPath filters: add logical operator support and tests #127

JsonPath filter expressions should support and be tested for common logical operators.

Work:

• Add parser support for !, &&, || (including parentheses) inside [?(...)].
• Ensure @ alone is treated as the current node in filters (not a property named "@").
• Add integration tests proving evaluation behavior.
• Add a focused unit test class validating JsonPathParseException exposes message/path/position details.