Fix Mach-O executables on macOS

[badlogic]

Adds LC_UUID to direct Mach-O executables so dyld will actually run them.\n\nChecked with:\n\nsh\nmake -C native/zero-c\n.zero/bin/zero run examples/hello.0\n

[vercel]

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[PeterXMR]

Confirmed this fixes the dyld error on macOS 26.4 / Darwin 25.4.0 arm64 — the salted hash + v4 bit-setting in macho_make_uuid are nice touches. Worth pairing the emit fix with a byte-level regression assertion so the bug can't silently come back. The assertMachOArm64Executable helper in conformance/run.mjs already runs for the direct exe test (around line 703) and doesn't currently scan load commands — adding a small walk catches missing LC_UUID even from a Linux sandbox where the binary can't be exec'd.
Suggested addition inside assertMachOArm64Executable, right after the existing asserts:
​js // dyld rejects Mach-O executables without LC_UUID on recent macOS. const ncmds = bytes.readUInt32LE(16); let cursor = 32; let hasUuid = false; for (let i = 0; i < ncmds; i++) { const cmd = bytes.readUInt32LE(cursor); const cmdSize = bytes.readUInt32LE(cursor + 4); if (cmd === 0x1b) { hasUuid = true; break; } cursor += cmdSize; } assert(hasUuid, "Mach-O executable is missing LC_UUID load command"); ​
Verified locally: trips on a binary with LC_UUID surgically removed, passes on the binary this PR produces.

[ctate]

Thanks for the PR @badlogic

Merged a fix in #55 - added you as a co-author