memdebug 0.6.0

Added

• Stand-alone programs. The release workflow now builds memdebug for Windows (x64), Linux (x64) and macOS (arm64) as a single file that needs no Python
  (PyInstaller), smoke-tests each on its own operating system, and attaches them to a GitHub release with a SHA256SUMS file and a build attestation. CI
  builds and tests them on every push. They are not code-signed (SmartScreen or Gatekeeper may warn), do not include Mem0, and still need git. See
  docs/releasing.md.

Fixed

• memdebug selftest in a build without its own Python: the tripwire checks could not start their tripwire and said SKIP, and "a hung process tree is killed"
  passed without testing anything (it started a program that exits at once). A stand-alone build now starts a hidden selftest-helper command with a fixed set
  of jobs instead. A source install is unchanged.