Automate releases using python-semantic-release

[dikshaa2909]

Automate Releases using python-semantic-release

Fixes #1992

This PR introduces an automated, CI-driven release workflow using
python-semantic-release to remove the remaining manual steps
(version bumping and tagging) from the current release process.

Technical approach

• Semantic version calculation based on Conventional Commits
• Automatic updates to:
  • pyproject.toml
  • scancodeio/__init__.py
  • CHANGELOG.rst
• Automatic creation of a vX.Y.Z Git tag on merge to main
• Reuse of the existing PyPI publishing workflow for build and distribution

Implementation

The goal is to make releases:

• Deterministic and reproducible
• Convention-based rather than manual
• Fully CI-managed
• Backwards-compatible with the existing publishing pipeline

No changes were made to the current PyPI workflow logic — this proposal
strictly automates the versioning and tagging layer.

This implementation is intentionally minimal and scoped, and can be
adjusted (tooling, branching model, changelog behavior) based on
maintainer preference.