The fixture builder only produced stored entries, so the vendored inflate
never ran under test. Add a small DEFLATE encoder and drive zip and
tar.gz entries through it: round-trips for fixed and dynamic huffman,
empty and large payloads, plus wrong CRC, wrong stated size, truncated
and corrupted streams, and a traversal name on a compressed entry.
Also cover the central directory and local header truncations that used
to raise.
