Fix compiler warnings for pip wheel builds (macOS + Windows) (#4989)

[alibeklfc]

Summary:

Fix compiler warnings that appear during pip wheel builds on macOS (AppleClang)
and Windows (MSVC).

macOS fixes (AppleClang):

1. Replace deprecated sprintf calls with snprintf in all three simdlib headers:

   • simdlib_emulated.h (4 call sites)
   • simdlib_avx2.h (4 call sites)
   • simdlib_avx512.h (3 call sites)

   AppleClang marks sprintf as deprecated. The fix replaces
   ptr += sprintf(ptr, fmt, val) with
   ptr += snprintf(ptr, (size_t)(res + sizeof(res) - ptr), fmt, val),
   where the second argument computes the remaining buffer space. This is
   safe and behavior-preserving: these are debug-only tostring() methods
   that format small integers/floats into 1000-2000 byte buffers, using at
   most ~256 bytes in the worst case (64 elements × ~4 chars). When output
   fits (which it always does), snprintf returns the same value as
   sprintf, so ptr advances identically.

2. Add missing override specifiers to fix -Winconsistent-missing-override:

   • IVFFlatScanner::scan_codes() in IndexIVFFlat.h
   • RaBitQHeapHandler::begin() and end() in IndexRaBitQFastScan.h
   • IDSelectorModulo::is_member() in faiss_example_external_module.swig

   These methods override virtual base class methods but lacked the
   override keyword. Adding it is purely declarative — no behavioral
   change, but enables compile-time checking if the base signature changes.

Windows fixes (MSVC):

3. Guard #pragma GCC diagnostic blocks with #if defined(__GNUC__) || defined(__clang__)
   to silence MSVC C4068 "unknown pragma" warnings in:

   • simdlib_emulated.h, simdlib_avx2.h, simdlib_avx512.h
   • IVFlib.cpp, PolysemousTraining.cpp

   The pragmas only control warning suppression (for -Wformat-nonliteral)
   and have zero effect on code generation. GCC/Clang still see them and
   behave identically; MSVC skips them (it doesn't have that warning anyway).

4. Fix %ld printf format specifiers in partitioning.cpp to use %zu for
   size_t and %" PRId64 " for int64_t (MSVC C4477: long is 32-bit
   on Windows, so %ld is wrong for both types). These are debug-only
   IFV printf calls gated behind a verbose flag.

5. Fix size_t to int narrowing in IndexIVFSpectralHash.cpp (MSVC C4267):
   std::make_unique<RandomRotationMatrix>(d_in, nbit_in) where d_in is
   size_t but the constructor takes int. Added static_cast<int>(d_in).
   Safe because d_in is vector dimensionality (typically 64-2048).

6. Fix pointer-to-long truncation in distances_sse-inl.h (MSVC C4311):
   Alignment check (long)ptr & 15 truncates 64-bit pointers on Windows
   where long is 32-bit. Changed to (uintptr_t)ptr which is correct
   on all platforms. The alignment test logic is unchanged.

Differential Revision: D98197799

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@alibeklfc has exported this pull request. If you are a Meta employee, you can view the originating Diff in D98197799.

[meta-codesync]

This pull request has been merged in 0759009.