boa-cat 0.7.1

Tree-walking ECMAScript interpreter built on ecma-syntax-cat. v0.7.1 promotes `expression::call_function` from `pub(crate)` to `pub` so embedder code (e.g. `web-api-cat`'s `addEventListener` / `dispatchEvent`) can invoke user-supplied JS callbacks from a `NativeFn` without duplicating the dispatch logic. No behavior change; one-line visibility unlock.