* Add zlib-rs as an autogated backend for zlib compression streams

Backs the shared ZlibStream core with zlib-rs (libz-rs-sys), the
memory-safe Rust implementation of the zlib C API, selected per stream by
the new compression-rs autogate. This covers both node:zlib and the web
CompressionStream/DecompressionStream API. The native chromium zlib
remains the default.

The z_stream ABI is identical between the two implementations, so the
integration is a function dispatch table (ZlibDispatch) consulted at
stream construction; node's dictionary/params escape hatches route
through the same table via ZlibStream::dispatch(). The zlib-rs symbols
are bridged from a translation unit that does not include the chromium
zlib headers, since chromeconf.h renames all standard zlib identifiers
(Cr_z_ mangling) - which is also why the unprefixed zlib-rs symbol names
are collision-free in the binary.

bench-zlib measures both backends on the streaming workload (1MB in 16KB
chunks, level 6): zlib-rs measures ~34% faster deflate and ~17% faster
inflate than the SIMD-enabled chromium zlib.

* Use zlib-rs throughout workerd

* Restore the zlib-rs rollout autogate

* Fix downstream zlib header dependencies

* Use zlib-rs for the zlib Bazel target

Route all zlib consumers through libz-rs-sys while retaining the Chromium zlib headers. Enable carry-less multiplication on x64 to preserve CRC32 performance.

* Avoid zlib module dependency on workerd

Use the canonical root repository label so the zlib overlay can depend on zlib-rs without changing zlib's module metadata.