build, Windows compatibility — absorb PR #74 fixes, resolve write ambiguity, add Windows CI runner

[steven-varga]

Problem

H5CPP does not compile on Windows. Three distinct blockers are known.

Blocker 1 — aligned_alloc unavailable on MSVC

h5cpp/H5Zpipeline.hpp allocates chunk buffers with aligned_alloc(), which is a C11 function not implemented by MSVC. Needs a platform shim:

#ifdef _MSC_VER
    ptr0.reset( static_cast<char*>(_aligned_malloc( block_size, H5CPP_MEM_ALIGNMENT )) );
#else
    ptr0.reset( static_cast<char*>(aligned_alloc( H5CPP_MEM_ALIGNMENT, block_size )) );
#endif

The h5::impl::free deleter in H5misc.hpp also needs a matching _aligned_free branch on MSVC. PR #74 already has a fix for this; absorb it.

Blocker 2 — h5::write name ambiguity (issue #58)

On Windows, headers like <winsock2.h> or <io.h> inject a POSIX write() into the global namespace. Every call site that resolves h5::write then becomes ambiguous. Fix: qualify all internal call sites, or wrap the HDF5/Windows headers to prevent the leakage.

Blocker 3 — H5Pset_fapl_direct undefined on Windows

h5cpp/H5Pall.hpp references H5Pset_fapl_direct unconditionally. This function requires O_DIRECT (Linux only). PR #74 already has the #ifdef H5_HAVE_DIRECT guard; absorb it.

Scope

• Absorb the three fixes from PR Compile on windows #74 (C2580, aligned_alloc, H5Pset_fapl_direct)
• Resolve h5::write / POSIX write ambiguity on Windows Clang and MSVC
• Add a Windows runner (windows-latest) to the CI matrix with MSVC or Clang-cl
• Verify find_package(HDF5) works with a pre-installed HDF5 on the Windows runner

References

• PR Compile on windows #74 — pending Windows VS2019 fixes (3 commits, never merged)
• Issue Clang (LLVM) Windows Issue #58 — Clang/LLVM Windows h5::write ambiguity