Tests: Added integration tests for GBNF parser (#6472)

* Added integration tests for GBNF parser to validate correctness of parsing, as well as correctness of string matching. Intended for use to pin behavior while working on performance improvements.

* Fixing whitespace errors and cleaning error message alert to be clearer.

* Removing hacky include to llama.cpp from grammar integration test now that needed functions are available via internal API.

* Comment cleanup.

* Reorganizing tests for readability.

* Cleaning up debug message to make a bit more sense.