Extract the Cypher parser into the standalone cypher-parser crate

Move the graph-independent Cypher front-end (lexer, recursive-descent
parser, AST, and error type) out of rubydex and depend on the standalone,
published `cypher-parser` crate from crates.io. The `rubydex` crate
re-exports the modules from `query::cypher`, so the executor, schema,
formatting, and tests keep their existing paths unchanged.

This separates the language front-end (parse a query string into an AST)
from execution against the rubydex graph, and lets the parser be
versioned, tested, and reused independently. Parser unit tests live in
the cypher-parser crate; rubydex keeps the executor and end-to-end tests.

Author: paracycle

rust/Cargo.lock

@@ -22,6 +22,7 @@ crate-type = ["rlib"]
 test_utils = ["dep:tempfile"]
 
 [dependencies]
+cypher-parser = "0.1"
 ruby-prism = "1.9.0"
 ruby-rbs = "0.3"
 url = "2.5.4"