Add unit test coverage for TSql180Parser error recovery, tokens, and filter edge cases #29

Problem

Several core parser and token processing utility classes have partial coverage in SonarCloud:

• TSql180Parser.java: 75.0% coverage (8 uncovered lines in syntax error recovery and quoted identifier toggle paths).
• TSqlWhitespaceTokenFilter.java: 80.7% coverage (10 uncovered lines in consecutive whitespace collapsing and comment token passing).
• TSqlParserToken.java & ParseResult.java: missing branch tests for null/error states and equality/hashcode edge cases.

Proposed Changes

• Add dedicated test cases in TSql180ParserTest covering syntax error callbacks and identifier quoting modes.
• Extend TSqlWhitespaceTokenFilterTest with multi-line block comments, adjacent comments, and EOF token boundaries.