chore(utils): add portable to_chars_double fallback for macOS

[rayandrew]

• Introduce to_chars_double wrapper that falls back to snprintf on macOS < 13.3
• Force CPM-built zstd on Apple to avoid deployment target mismatches
• Update version patch to 8

[Copilot]

Pull request overview

This PR improves macOS portability by avoiding unsupported std::to_chars(double) on older Apple deployment targets and by ensuring zstd is built in a way that matches the wheel’s deployment target (avoiding host-library mismatches during wheel repair).

Changes:

• Add a dftracer::utils::to_chars_double wrapper with an Apple fallback to snprintf for macOS deployment targets < 13.3, and use it in bloom_visitor.cpp.
• On Apple, pin CMAKE_OSX_DEPLOYMENT_TARGET from MACOSX_DEPLOYMENT_TARGET in the CMake cache and prefer CPM-built zstd over system zstd.
• Bump project version patch from 7 to 8.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/dftracer/utils/utilities/composites/dft/visitors/bloom_visitor.cpp	Switch double formatting to a portable to_chars_double wrapper.
include/dftracer/utils/core/common/to_chars.h	New portable double-to-string helper with macOS fallback.
CMakeLists.txt	Cache-declare CMAKE_OSX_DEPLOYMENT_TARGET from environment on Apple; bump patch version.
cmake/modules/Dependencies.cmake	Avoid system zstd on Apple and pass deployment target into CPM zstd build.

Comments suppressed due to low confidence (1)

cmake/modules/Dependencies.cmake:1405

• On Apple, find_package(zstd ...) is skipped, but zstd_FOUND can still be TRUE from a previous configure (it’s also written to the cache later in this function). In that case this if(zstd_FOUND) branch will run and can silently select a cached/system zstd, defeating the "always CPM-build on Apple" intent. Consider explicitly forcing zstd_FOUND to FALSE (and clearing cached include/lib hints) when APPLE, or changing the condition to only honor zstd_FOUND when NOT APPLE.

  if(NOT APPLE)
    find_package(zstd QUIET CONFIG)
    if(NOT zstd_FOUND)
      find_path(zstd_INCLUDE_DIRS NAMES zstd.h)
      find_library(zstd_LIBRARIES NAMES zstd)
      if(zstd_INCLUDE_DIRS AND zstd_LIBRARIES)
        set(zstd_FOUND TRUE)
      endif()
    endif()
  endif()

  if(zstd_FOUND)
    message(STATUS "Found system zstd")
    if(DEFINED zstd_LIBRARIES)

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