Fix the API check for Rust doc examples

An AI wrote usage docs for your Rust crate. The prose is good, but one example calls client.fetch_all() and another RetryPolicy::exponential(), and the crate has neither. They look like real methods because they follow the usual naming. Until every example runs as a doctest in CI, your team checks the examples against the crate's real symbol table.

An assistant wrote find_hallucinated_api_calls(known_symbols, example_lines). It is in the editor. It has a bug. Find it and fix it.

Input and output:

• known_symbols: every callable the crate really has, written as it is called: a bare method name like fetch_page, or a path like Client::connect.
• example_lines: the code lines of the doc examples.
• Return each name the examples call that is not a known symbol, once each, sorted by plain character order.

Rules the tests check:

• Every ( in a line is a call site. Its name is the run of characters just before the ( made only of ASCII letters, digits, _ and :. So client.fetch_all( names fetch_all, and RetryPolicy::exponential( names RetryPolicy::exponential. Remove any : at the start of the name, then check it against the rules below.
• Skip a call site whose name is empty, as after a macro like println!( or in (b + c).
• Skip the keywords if, while, for, match, return, let and fn.
• Skip a definition: the name follows the word fn with only spaces or tabs between them, as in fn main(. fn must be a whole word, so the character before it, if any, is not a letter, digit, _ or :.
• Trim each known symbol. A call is real only when its whole name equals a known symbol exactly, case included. Client::new being known does not make Config::new real.