Fix: Add ETS buffering for telemetry events in TelemetryListener

[techvoyagerX]

This PR improves the handling of high event rates in the Phoenix Live Dashboard by introducing an ETS-based buffering system in TelemetryListener. It ensures that events are buffered efficiently and prevents system overload by trimming the buffer when necessary.

Key changes:

• Added ETS table for event buffering.
• Introduced buffer overflow handling to maintain system stability under high loads.
• Cleaned up ETS table on process termination.

These updates ensure the metrics page continues to function smoothly even under high telemetry event loads.

[josevalim]

Thank you for the PR but I am confused. We never read from the table. How does this help with buffering?