Dependency maintenance: consume Serializable 0.10.1 and Event 5.8.1

[LK-Simon]

Summary

Complete the Serial 0.5.1 bug-fix release against the final dependency cascade produced after Serializable 0.10.1.

Scope

• Continue from the existing Serial Bug: EventMonitor structured diagnostics can crash under low memory or hostile payloads #7 bug-fix work and prepare the final 0.5.1 candidate.
• Consume released Serializable 0.10.1 instead of the temporary bug-fix commit once available.
• Update the validated Event baseline from 5.8.0 to 5.8.1 after Event's dependency refresh.
• Update current README, dependency chart, examples/tests/workflows, CHANGELOG and package metadata so self/dependency versions are consistent.
• Preserve all Serial integrations as opt-in.

Dependency direction

Serial remains a downstream diagnostics/operator layer. It may consume Command, Security, Sockets, ESP-Now, Event, Serializable, Timing and Threads integrations, but none of those libraries should depend on Serial.

Release order

Serializable 0.10.1 -> Units 0.2.2 -> Timing 2.2.3 -> Threads 3.1.3 -> ESP-Now 0.5.1 / Event 5.8.1 -> Serial 0.5.1.