• PyO3 Rust created upgraded from 0.24 to 0.25. (#273)
• We now use Py_REFCNT(obj) instead of accessing (*obj)->ob_refcnt directly.
  This fixes a nogil / multi-threaded compile error. (#201, #275)
• A zstandard commit to fix qsort detection on BSD operating systems
  has been backported. (#272)
• The PYTHON_ZSTANDARD_IMPORT_POLICY environment variable now has leading
  and trailing whitespace stripped. Values like cffi and cffi are
  now equivalent to cffi.
• The CI jobs for building wheels have been overhauled to always use
  cibuildwheel and uv (where possible). This change should be backwards
  compatible. But wheel building for this project has historically been
  fragile and there may be unwanted changes. We're optimistic that standardizing
  on uv (except for musllinux ppc64le and s390x where uv isn't available)
  will lead to more stability over time.
• CI now runs tests against the wheels we distribute. Previously, we ran
  tests against a separate build that was theoretically identical. But the
  builds may have been subtly different, leading to preventable bugs in our
  wheels. (Enabling this test coverage did not uncover any failures.)
• The pyproject.toml build backend has been switched from
  setuptools.build_meta:__legacy__ to setuptools.build_meta.
• The setuptools build dependency has been upgraded from <69.0.0 to >=77.0.0.
  Modern versions of setuptools broke
  --config-settings=--build-option=... as part of implementing PEP 660.
  A workaround is to use --config-settings=--global-option=... instead.
  --global-option apparently is deprecated and the setuptools folks have yet
  to figure out how to thread config settings into setup.py invocations.
  (--build-option is sent to the build_wheel command but not the
  build_editable command.)
• Python 3.14 wheels are now built with manylinux_2_28 (versus
  manylinux2014) for older Python versions. This may raise the minimum
  glibc version, effectively dropping support for Debian 8 and 9, Ubuntu
  13.10 through 18.04, Fedora 19 to 28, and RHEL/Centos 7. However, in
  practice most platforms don't container newer glibc symbols and are still
  ABI compatible with manylinux2014 and glibc 2.17.
• We now require cffi >= 2.0.0b on Python 3.14. <3.14 still requires 1.17.
  (#274)
• The cffi backend is now automatically disabled for free-threaded builds
  on Python <3.14, as cffi didn't implement free-threaded support until
  the 2.0 release. (#274)
• Added CI coverage for free-threaded CPython 3.13 and 3.14. We do not yet
  formally support free-threaded builds. (#276)
• The C and Rust backends now declare the GIL as unused.
• The pythoncapi_compat.h file has been upgraded to the latest version. (#278)
• setup.py now depends on packaging and uses packaging.version.Version
  for version comparisons. This removes some deprecation warnings from usage of
  legacy distutils Version classes.
• Relax run-time libzstd version checking in C extension from exactly 1.5.7
  to >=1.5.6. (#254, #267)
• C extension types now (correctly) declare their fully qualified type names
  as zstandard.backend_c.* versus zstd.* before. The names have been
  subtly broken for years. We believe the only practical exposure to this change
  is via pickling (possibly encountered when using the multiprocessing or
  concurrent.futures packages), which would fail to pickle types like
  ZstdError before since the fully qualified type name referenced an
  incorrect and likely missing package (zstd). (#248)