Problem

No :telemetry events are emitted anywhere in the library. Operations are invisible to observability stacks (Prometheus, DataDog, etc.).

Impact

• Cannot monitor pack generation time, object counts, error rates
• Cannot set alerts on storage growth or protocol failures
• Production debugging requires log diving instead of dashboards

Acceptance Criteria

• :telemetry dependency added
• Events emitted for: object read/write, pack read/write, ref update, protocol operations
• Each event includes relevant metadata (duration, size, object type, backend)
• Event names follow telemetry naming conventions ([:ex_git_objectstore, :object, :write])
• Documentation of all emitted events and their measurements/metadata
• No performance regression from telemetry instrumentation