Error: better error mechanism is needed

[yuanbohan]

Use String in terms of easy coding for now. Chumsky can be a good choice. This should include at least:

• Parser
• Lexer

[yuanbohan]

ParseError from cfgrammar SHOULD be friendlier to Prometheus users

[vvv]

See also winnow = toml_edit + combine + nom. chumsky didn't meet their performance and ergonomics criteria. (It still may be a good choice for promql-parser though.)