Conflict in crates/codecs/src/other.rs with #2769, which added gated_first_frame (a GIF's
first frame bounded by max_pixels before decode). Both gates are kept: #2769's runs first in
decode, then check_size and check_fillable; the two test modules are merged into one.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016TuX1qw9ieyuJ1ZFrrUxzc