use statically build libraries instead of syso files

[pk910]

Problem

The existing .syso file approach was causing persistent CGO warnings for all downstream projects:

loadinternal: cannot find runtime/cgo

This warning appeared even with CGO_ENABLED=1 because Go's linker detected native code in .syso files but couldn't find the CGO runtime. The warning was harmless but annoying and unprofessional for library users.

Solution

Replaced .syso files with proper CGO bindings using pre-built platform-specific static libraries.

What Changed

1. Removed problematic files:

   • All *.syso files
   • Assembly wrapper files (wrapper_*.s)
   • Platform-specific Go files (bindings_*.go)

2. Added platform-specific CGO bindings:

   • cgo_linux_amd64.go - Linux x86_64 with AVX2/AVX512/SHANI optimizations
   • cgo_linux_arm64.go - Linux ARM64 with SHA2 optimizations
   • cgo_darwin_arm64.go - macOS Apple Silicon with SHA2 optimizations
   • cgo_windows_amd64.go - Windows x86_64 with AVX2/AVX512/SHANI optimizations
   • cgo_fallback.go - Pure Go fallback when CGO disabled

3. Pre-built static libraries:

   • lib/linux_amd64/libhashtree.a - Native Linux x86_64 build
   • lib/linux_arm64/libhashtree.a - Cross-compiled ARM64 build
   • lib/darwin_arm64/libhashtree.a - Native macOS ARM64 build
   • lib/windows_amd64/libhashtree.a - Native Windows MinGW build

4. GitHub Actions workflow:

   • Builds libraries on appropriate native systems (ubuntu-22.04, macos-14, windows-latest)
   • Uses compatibility flags for broader platform support
   • Automatically builds libraries when source changes
   • Uploads build artifacts for simple copy & commit back to repo on demand

5. Restored original CPU feature detection:

   • x86_64: supportedCPU = hasAVX2 || hasShani || hasAVX512
   • ARM64: supportedCPU = hasShani (improved from original true)

[pk910]

should fix #7 & #52