Add optional telemetry observability backend

[Gabriel-Darbord]

Summary

• add an MCP-owned observability backend protocol with a no-op default, keeping telemetry disabled unless explicitly enabled
• improve JSON monitoring data with normalized tool-call records, dispatch paths, input/output sizes, lifecycle timestamps, event kinds, and safer atomic exports under image-local pharo-local/mcp/observability
• remove TinyLogger from core observability; MCP now owns its local in-memory log entries and JSONL file appends directly
• add optional OpenTelemetry support through the Telemetry group while keeping OpenTelemetry out of the default dependency surface
• update monitoring/dashboard tests and user documentation for the new observability model