JS-018: no generic zlib — bind `ZINFInflate` / `ZINFDeflate`

Now: DONE

Only pack-internal inflate (PACK.inflate) and delt.apply are reachable; there is no standalone zlib, so a loose git object or any gz stream can't be (de)compressed from JS. Method: Issues.

Input

Context

js/cont.cpp binds PACK.inflate (pack-entry only) and delt.apply (delta only); no general zlib leaf is exposed.
Reading a loose object (.be/.../xx/yyyy, zlib) from JS is impossible — surfaced by the be status review (object-store reads need it).
dog/git/ZINF.h ZINFInflate(u8s into, u8cs zipped) / ZINFDeflate already exist — bindable leaves, no new dog work.

Goals

zlib.inflate(src, out) / zlib.deflate(src, out) over Bufs.

Constraints

Marshal over ZINF; write into out.idle(), commit with out.fed(n) — mirror the existing pack.inflate / delt.apply shape.
New zlib global (or under io); leaf-only, no buffers held.

WIP

Design decisions

(open) zlib.inflate(src, out) and zlib.deflate(src, out), both returning the byte count and advancing out.

TODOs

Repro-first: deflate→inflate round-trips a buffer; a real loose object inflates to its known bytes.
Bind the two ZINF leaves.

Blockers

None.

Outcome

(pending)