[release] Release 0.2.1

[gregnazario]

Made-with: Cursor

[Copilot]

Pull request overview

Release prep for decibel-python-sdk v0.2.1, updating the package/version metadata and introducing a changelog entry for the release.

Changes:

• Bump project version from 0.2.0 to 0.2.1.
• Update uv.lock to reflect the new editable package version.
• Add CHANGELOG.md documenting changes in 0.2.1 (and noting 0.2.0).

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 1 comment.

File	Description
pyproject.toml	Updates the package version to 0.2.1 for the release.
uv.lock	Updates the editable package entry version to match 0.2.1.
CHANGELOG.md	Adds a Keep a Changelog–style changelog with a 0.2.1 entry and links.

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[Copilot]

The project version is bumped to 0.2.1 here, but the runtime-exposed decibel.__version__ is still hard-coded as 0.1.0 (see src/decibel/_version.py:1). For a release, please update that constant (or derive it from package metadata) so decibel.__version__ stays in sync with the published package version.