Allow "new" as identifier in non-expression contexts

[cemrehancavdar]

Problem

new is currently only recognized as the operator in C++ new expressions
(e.g., new SomeType(args)). When used as a plain identifier — which is valid
Cython and common in real-world code — the parser produces an error.

Example from numpy/random/_generator.pyx#L943:

new = cdf.searchsorted(x, side='right')
new = new.take(unique_indices)

Fix

Add "new" to the keyword_identifier rule in grammar.js. This allows
new to be used as an identifier at lower precedence (-3) while preserving
the existing new_expression rule at precedence 23 for C++ new Type(args)
syntax.

Changes

• grammar.js: add "new" to keyword_identifier choice list (1 line)
• test/corpus/expressions.txt: add "New as identifier" test case

All 155 tests pass (154 existing + 1 new).