Adds executable and object file signatures: ELF, Mach-O (thin and universal), PE/COFF, WebAssembly, ar, and zstd.
The Format* constants are now exported so callers can switch on Result.Format without string literals.
Universal Mach-O is disambiguated from Java class files (shared CA FE BA BE prefix) via the architecture count. PE detection follows e_lfanew within the 512-byte sniff window.