Dependency maintenance: consume ESPressio Units 0.2.3

[LK-Simon]

Summary

Refresh ESPressio Timing after the Serializable 0.10.2 downstream cascade.

Scope

• Prepare ESPressio Timing 2.2.4.
• Update the Units baseline to 0.2.3 once released.
• Update current README, changelog, dependency chart, metadata, and validation references.
• Keep Serializable transitive/opt-in through Units; do not add a direct Serializable dependency.

Release

Target patch release: 2.2.4.