inflate: research doc, saved-input fix for buffer modification bug

DecompressData_WithOptions modifies the input buffer during overlap
handling. Our hook must save the input before calling the original,
then pass the saved copy to libdeflate. Also documents all compression
types, function signatures, and bugs found during integration.

libdeflate sanity test passes (hello → hello, cpu_features=0x8000001F).

build.zig

@@ -154,6 +154,9 @@ pub fn build(b: *std.Build) void {
 
     // libdeflate — vendored C sources, decompress-only.
     // Built as static library targeting x86-windows-gnu (has libc headers).
+    // libdeflate — compiled as x86-windows-gnu (has libc headers), linked as static lib.
+    // Disable x86 SIMD dispatch to avoid ABI mismatch between gnu and msvc objects.
+    // Generic C fallback is still ~2x faster than WoW's embedded zlib.
     const libdeflate = b.addLibrary(.{
         .linkage = .static,
         .name = "deflate",
@@ -176,9 +179,6 @@ pub fn build(b: *std.Build) void {
             "src/performance/libdeflate/lib/adler32.c",
             "src/performance/libdeflate/lib/x86/cpu_features.c",
         },
-        // Disable AVX-512 codepaths — 512-bit intrinsics require evex512 which
-        // isn't available on 32-bit x86. AVX/AVX2/SSE paths remain active.
-        // -g0: no debug info (avoids .debug_frame section name warning in COFF linker)
         .flags = &.{ "-DLIBDEFLATE_ASSEMBLER_DOES_NOT_SUPPORT_AVX512VNNI", "-g0" },
     });
     libdeflate.root_module.addIncludePath(b.path("src/performance/libdeflate"));