ref: Revamp feature flags

[jan-auer]

Restructures all feature flags and removes features that are no longer
supported:

1. To enable the cadence adapter, use the cadence feature directly now.
   Before, it was called cadence-adapter.
2. The sentry feature has been removed since this support for metrics via the
   Sentry SDK is deprecated and pending removal.
3. All optional dependencies like serde are no longer features.
4. Disables the binary (main.rs) when there's no cli feature