fix(binder): keep a variable's name when an arithmetic identity returns it

[zahariash]

This work was produced with the help of language models.

Fixes #1247.

UNWIND [1, 2] AS x WITH x + 0 AS y, x RETURN y, x returned two columns named x, as did RETURN x, x + 0. A projection names each item by setting the alias on its expression, and a variable reference binds to the scope's own object, so when x + 0, x * 1, x - 0 or x / 1 simplified to that object, the alias renamed the variable.

Fix. An arithmetic identity over a scope expression stays as written, so the alias lands on +(x,0). A scope expression is also never simplified again, and NOT NOT does not unwrap a NOT taken from the scope; either would return a part of the kept expression that is no longer in scope: CASE WHEN true THEN m END after WITH n + 0 AS m then ran the aggregate again, and NOT z after WITH NOT b AS z fails on main today with "Cannot evaluate expression with type VARIABLE". Boolean, CASE and cast simplifications still return the operand and still rename it, as plain WITH x AS y, x does; that is unchanged and tracked in #1287. Property references are copies, so n.id + 0 = 1 still becomes an index lookup.

Tests. projection/simplified_variable_alias.test: ArithmeticIdentityOverVariableKeepsAlias checks the column names of the issue's three queries and of RETURN x, x + 0; on main they are x, x, m, m, x, x. SimplifiedScopeExpressionReferencedLater and SimplifiedNodeStaysPattern reference a kept x + 0, b AND true, NOT b or node from a later CASE, AND, NOT, ORDER BY or MATCH; the NOT z query fails on main, the rest pin the two rules. Full suite: no failures.