boa-cat 0.7.2

Tree-walking ECMAScript interpreter built on ecma-syntax-cat. v0.7.2 lands three integration tests pinning down the existing `new SomeNativeFn(args)` dispatch path: `expression::construct` allocates a fresh empty Object as `this`, hands it to `call_function`, and honours the spec's "return the Object the constructor produced, else fall back to `this`" semantics. Embedders (e.g. `web-api-cat`'s `Event` / `CustomEvent` constructors) can now rely on this surface without reverse-engineering the implementation. No source change.