idftool is now at https://github.com/nebkat/idftool.

- Remove idftool package, entry point, spec files, Makefile, setup.py, CONTRIBUTING.md
- Rename package from nebkat-esp-idf to esp-idf-defs
- Switch versioning to setuptools-scm (git tags)
- Replace PyInstaller CI with two-stage build+publish workflow for PyPI
  (publish job gated behind pypi GitHub environment for manual approval)
- Move ESPLoader import in partitions.py under TYPE_CHECKING so esp-idf-defs
  has no runtime dependency on esptool