Return per-call read/write counts from zlib execute

[robknopf]

Since the typed zip rewrite (#1277), ZLibCompress::execute and ZLibUncompress::execute return z_stream::total_in / total_out. Those totals accumulate across calls, but haxe.zip.Compress.execute / Uncompress.execute callers, including Uncompress.run, treat read / write as the progress of the current call.

As a result, haxe.zip.Uncompress.run(bytes) throws OutsideBounds once the decompressed output exceeds its 64K buffer. On the second iteration write reports the running total, so addBytes(tmp, 0, r.write) reads past tmp. Chunked execute loops also re-read input, because pos += r.read advances by the total.

Reproduction

final bytes = haxe.io.Bytes.alloc(300000);
for (i in 0...bytes.length) bytes.set(i, (i * 7 + (i >> 9)) & 0xff);
haxe.zip.Uncompress.run(haxe.zip.Compress.run(bytes, 9)); // Error : OutsideBounds

This works on haxelib hxcpp 4.3.2 and fails on releases from v4.3.106 onward. Single-call use (output under 64K) is unaffected, which is why the existing testCompress passes.

Change

execute now returns the per-call counts, src.length - avail_in and dst.length - avail_out, in both files. I also added testCompressMultipleBuffers to test/std, which round-trips 300 KB through Uncompress.run and through a chunked execute loop with a 4K output buffer.

Testing

On Linux x86_64 (GCC 13.3, Haxe 4.3.7), I ran the same assertions as a standalone program: Uncompress.run over 64K, chunked decode, chunked compress into 512-byte buffers, and a 1 MiB real-world asset. Before the change they fail with OutsideBounds; after it they pass. I couldn't run the full test/std suite locally because it doesn't compile against utest 1.13.2 (Assert.exception at Test.hx:452, unrelated to this change).