[JayPokale]

The AST, the semantic analyzer and the DataFusion planner already handle ValueExpression::Arithmetic (#13, #68), but the parser never builds it, so any query with an arithmetic operator fails to parse:

MATCH (p:Person) RETURN p.age + 1 AS next_age
Cypher parse error at position 30: Unexpected input after query: + 1 AS next_age

This adds arithmetic to value_expression:

• + and - bind looser than *, / and %; all are left-associative (10 - 4 - 3 is (10 - 4) - 3).
• Parenthesized sub-expressions: (p.age + 1) * 2.
• Works anywhere a value expression is accepted, so WHERE p.age / 5 - 1 >= 5 works too.
• COUNT(*) is unaffected, because the * argument is matched before the argument list is parsed.

Tests:

• Parser unit tests for precedence, associativity, parentheses, n.age-1 without spaces, arithmetic inside a WHERE comparison, and count(*) * 2.
• tests/test_arithmetic_expressions.rs runs RETURN and WHERE arithmetic end to end on the DataFusion executor and checks the values.

Commands run in crates/lance-graph: cargo test (all unit, integration and doc tests pass), cargo fmt --all -- --check, cargo clippy --all-targets -- -D warnings.

I used an AI assistant (Claude) while working on this; I reviewed and tested the change.