zlib: decode concatenated zstd frames

[agape1225]

A single write to a zstd decompression stream can hold several
concatenated zstd frames. The zstd format explicitly allows this and
zstdcat decodes it, but Node stopped after the first frame whenever
the frame boundary fell inside one input buffer:

const zlib = require('node:zlib');
const data = Buffer.concat([
  zlib.zstdCompressSync(Buffer.alloc(2000, 0x41)),
  zlib.zstdCompressSync(Buffer.alloc(2000, 0x42)),
]);
zlib.zstdDecompressSync(data).length; // 2000, expected 4000

ZstdDecompressContext::DoThreadPoolWork ran a single
ZSTD_decompressStream call, and the JS processing loop treated the
leftover input with free output space as the end of the stream. gzip
already handles concatenated members correctly, and the reporter of
the issue hit this in practice after ~3 GB of streamed data.

This keeps decoding across frame boundaries while input is pending and
output space is left, mirroring the gzip multi-member loop. When
rejectGarbageAfterEnd is set, it stops after the first frame so the
trailing frames are still reported as junk — the option is now wired
through to the zstd decompression context for that purpose.

rejectGarbageAfterEnd: false + trailing bytes that are not a valid
frame now produces a decode error instead of being silently ignored,
which matches gzip's behavior for trailing non-padding garbage.

Fixes: #64741

This re-does #64748 by @lazerg (closed for lack of review) on top of
current main, keeping the same approach; credited via Co-authored-by.

🤖 Generated with Claude Code

[jasnell]

duplicates #65865

[codecov]

Codecov Report

❌ Patch coverage is 90.47619% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.18%. Comparing base (2987a59) to head (f93a2bb).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_zlib.cc	90.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65911      +/-   ##
==========================================
+ Coverage   90.16%   90.18%   +0.02%     
==========================================
  Files         771      771              
  Lines      265097   265077      -20     
  Branches    50358    50344      -14     
==========================================
+ Hits       239026   239062      +36     
+ Misses      17011    16963      -48     
+ Partials     9060     9052       -8     

Files with missing lines	Coverage Δ
lib/zlib.js	98.14% <100.00%> (+<0.01%)	⬆️
src/node_zlib.cc	79.72% <90.00%> (+0.19%)	⬆️

... and 36 files with indirect coverage changes

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