Add a native find() method to unique associative containers (e.g., Map)
that returns the mapped value if the key exists, or an undefined
Boxed_Value if not. This allows checking for key existence without
mutating the container (unlike operator[]) or requiring exception
handling (unlike at()).
Co-authored-by: leftibot <leftibot@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
