fix: undo release 0.3.0, no changes

[paolodamico]

Bug in the release process, undoing release 0.3.0 which has no changes, before it gets published.

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Note

Low Risk
Release-metadata-only change that reverts an incorrect version bump; low risk aside from potentially affecting downstream packaging/version expectations.

Overview
Corrects an erroneous 0.3.0 release by removing the 0.3.0 section from CHANGELOG.md and leaving the project at 0.2.12.

Reverts the crate/workspace version back to 0.2.12 in Cargo.toml and aligns Cargo.lock package entries (bedrock, bedrock-macros, uniffi-bindgen) to match.

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