Improved telemetry

[JackHopkins]

Is your feature request related to a problem? Please describe.
Too many anonymous telemetry calls are being sent. This creates unnecessary overhead.

Describe the solution you'd like
Reduce the number of calls made, and make each one more informative while still being anonymized.
E.g:

• Post an 8-byte hash of the API key
• Post only the function signatures, not the actual inputs.
• Only post when flushing the buffer to disk.