zlib: add crc32c

[pipobscure]

Add zlib.crc32c(data[, value]), which computes the CRC-32C checksum (Castagnoli polynomial, RFC 3720 section 12.1). CRC-32C has better error detection properties than the CRC-32 of zlib.crc32() and is the checksum required by many current protocols, formats and services, among them:

• iSCSI header and data digests (RFC 7143)
• SCTP packet checksums (RFC 9260)
• iWARP MPA framing (RFC 5044)
• NVMe/TCP header and data digests
• ext4, Btrfs and XFS metadata checksums
• the Snappy framing format
• Apache Kafka record batches
• LevelDB and RocksDB block checksums
• TensorFlow TFRecord files
• Google Cloud Storage and Amazon S3 object checksums

Implementing any of these in JavaScript currently needs a userland CRC-32C, which is far slower than native code.

The function mirrors zlib.crc32(): it accepts a string (encoded as UTF-8) or an ArrayBufferView, takes an optional 32-bit unsigned starting value so a checksum can be continued across chunks, and has a V8 fast API path.

The checksum is computed by absl::ExtendCrc32c() from the bundled Abseil, which is already built and linked into node, so this adds no new dependency and no new checksum implementation. absl_crc32c is added to the libraries linked with --shared-abseil.

Abseil selects its hardware-accelerated CRC-32C path (SSE4.2 and PCLMULQDQ on x64, the CRC32 and PMULL extensions on arm64) at compile time, so with node's default compiler flags the portable table-driven implementation is used. It runs at about the same speed as zlib.crc32() (about 6.5 GB/s on a recent x64 machine), while the hardware path reaches about 38 GB/s. Builds whose target CPU baseline already includes those instructions get the hardware path without changes. Enabling it for generic builds is left out on purpose: on x64, Abseil uses the accelerated code for unrecognized CPUs without a runtime feature check, so compiling it in unconditionally would fault on CPUs without SSE4.2.

I had agentic help here, but I did review and check every single line.

[nodejs-github-bot]

Review requested:

• @nodejs/performance

[codecov]

Codecov Report

❌ Patch coverage is 90.62500% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.49%. Comparing base (f513ec7) to head (fbeb1b3).
⚠️ Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_zlib.cc	85.00%	0 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66828      +/-   ##
==========================================
- Coverage   90.49%   90.49%   -0.01%     
==========================================
  Files         797      797              
  Lines      277686   277824     +138     
  Branches    53362    53376      +14     
==========================================
+ Hits       251292   251413     +121     
+ Misses      16796    16795       -1     
- Partials     9598     9616      +18     

Files with missing lines	Coverage Δ
lib/zlib.js	98.14% <100.00%> (+0.01%)	⬆️
src/node_zlib.cc	80.28% <85.00%> (+0.07%)	⬆️

... and 38 files with indirect coverage changes

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