Consider telemetry

[utaal]

We'd definitely want to only enable telemetry as an opt-in feature.

This would be to either to collect stats on verification failures, times, and error messages encountered. We should also consider collecting stats on panics.

Folks have also suggested that we could (with very explicit opt-in) collect sources and/or SMT files for proofs that fail or time out.

NOTE: this was discussed at the [Verus all-hands]