Audit fs/path/os/zlib for Node 24 and Haxe 4

[kevinresol]

Summary

• Completes the Section 2 Node.js v24 + Haxe 4 audit for fs (+promises), path, os, zlib, and related sys/Sys/haxe.zip surfaces.
• Adds missing public APIs: Fs.openAsBlob, Fs.promises, Fs.mkdtempDisposableSync, FsPromises.mkdtempDisposable, StatWatcher, experimental Utf8Stream, Zstd compress/decompress (classes + convenience methods), Zlib.constants, Stats millisecond fields, Promise overloads on Dir.close/Dir.read, FSWatcher.ref/unref, and glob cwd as String|URL.
• Marks legacy Fs.F_OK/R_OK/W_OK/X_OK as @:deprecated in favor of Fs.constants.*.
• Drops Haxe 3 #if haxe4 / haxe_ver gates in this section (Haxe 4+ only) and tightens Dynamic where safe (Fs.write/writeSync string overloads); remaining Dynamic sites are marked TODO(section-2) / TODO(section-6).

Remaining TODOs (inline)

• Typed Fs.promises module value type (currently Dynamic)
• realpath.native / realpathSync.native function properties
• Typed ZlibConstants (currently DynamicAccess<Int>)
• Stats bigint nanosecond fields (atimeNs etc.)
• Node ErrnoException typing for sys/Sys catch sites
• FileHandle.readableWebStream → typed ReadableStream (coord with section 6)
• Utf8StreamOptions.fs mock object typing

Test plan

• Targeted Haxe compile of audited modules (-D nodejs + allowPackage('sys'))
• haxe completion.hxml succeeds
• Spot-check new APIs against Node.js v24 docs (openAsBlob, mkdtempDisposable*, Zstd, Utf8Stream)
• Confirm no regressions for existing fs/promises / zlib Brotli callers