Release v2.0.2

[jhnwu3]

This pull request prepares the PyHealth 2.0.2 release. It introduces a comprehensive changelog, updates version numbers across the project, and improves the version bumping tool to keep version metadata consistent. The most important changes are grouped below.

Release and Documentation:

• Added a detailed CHANGELOG.md documenting all notable changes, new features, datasets, models, tasks, fixes, and infrastructure updates for version 2.0.2.

Versioning Updates:

• Updated the version number to 2.0.2 in both pyproject.toml and pyhealth/__init__.py to reflect the new release. [1] [2]

Tooling Improvements:

• Enhanced tools/bump_version.py to:
  • Ensure the __version__ variable in pyhealth/__init__.py is always kept in sync with the version specified in pyproject.toml. [1] [2]
  • Only update the [project] version line in pyproject.toml, avoiding accidental changes to unrelated version fields.
  • Fix logic for finding the next available version, improving handling of both normal and pre-release versions. [1] [2]