Add parser benchmarks

[dmitriplotnikov]

Add parser benchmark suite in parser/bench to evaluate parser performance across 4 coarse-grained categories:

• Simple: Common, representative CEL expressions (arithmetic, comparisons, logical, conditionals, indexing, literals).
• Complex: Deeply chained expressions, nested parentheses, message constructors, operator precedence chains.
• Macros: Comprehension and receiver macros (has, all, map, filter, exists_one, optMap).
• Errors: Representative syntax error cases covering invalid tokens, unclosed delimiters, reserved keywords, and deep chain errors.

[TristonianJones]

There are some existing benchmarks under parser_test.go within the BenchmarkParse path. Are these covering what you're looking for? Or could the existing tests be annotated with the categories you'd like to see?