zlib: validate flush kind for brotli streams

[Ic3b3rg]

Summary

BrotliCompress.flush(kind) and BrotliDecompress.flush(kind) forwarded any kind value to the native encoder/decoder without validating it. Passing Z_FINISH (4) or Z_BLOCK (5) caused the process to spin at 100% CPU
indefinitely, because brotli has no matching operation and the loop never makes progress.

This PR validates kind against the brotli operation range [0, 3] before the fake-chunk is queued, and throws ERR_OUT_OF_RANGE on invalid input. The check mirrors the validation already done in the ZlibBase constructor for options.flush and options.finishFlush.

Scope

Validation is intentionally limited to brotli streams. Zlib and zstd flush() calls are unchanged. Internal callers of flush() were audited and the only one (Zlib.prototype.params calling flush(Z_SYNC_FLUSH=2)) is in range for brotli — no regression.

Observable behaviour changes (brotli streams only)

Call	Before	After
flush(4) (Z_FINISH)	hang 100% CPU	throws ERR_OUT_OF_RANGE
flush(5) (Z_BLOCK)	hang 100% CPU	throws ERR_OUT_OF_RANGE
flush(6) (Z_TREES)	throws ERR_INVALID_ARG_TYPE (incidental, from write(undefined))	throws ERR_OUT_OF_RANGE
flush(0..3) (valid brotli ops)	works	works
flush(), flush(cb)	works (uses default)	works (uses default)

Cross-runtime note

Bun is fixing the same bug on their side (oven-sh/bun#31505) but plans to throw ERR_INVALID_ARG_TYPE to match the current incidental behaviour of flush(6) on Node. This PR chooses ERR_OUT_OF_RANGE for internal consistency with the checkRangesOrGetDefault validation already used elsewhere in lib/zlib.js.

Fixes: #63701