feat(s2n-quic-core): add nominal counter aggregations

[camshaft]

Description of changes:

This change adds the ability to emit counter metrics based on individual variants. For example, we want a total number of errors for each type of error that can occur.

The event specifies this aggregation as such:

struct MyEvent {
    #[nominal_counter("state", "")]
    state: State,
}

enum State {
    A,
    B,
    C,
}

There will be a total of 4 counters registered for this particular event: 1 for the overall event, and then an individual counter for each possible variant inside of State.

Testing:

The dc path secret map tests can be run to show it all working:

$ S2N_LOG=trace cargo test -p s2n-quic-core -p s2n-quic-dc --features probe-tracing -- map::event_tests::control_packets --nocapture
...
2024-11-06T22:36:20.268288Z TRACE s2n_quic_core::event::metrics::aggregate::probe::dynamic::counter::record: id=41 name="replay_detected_packet_accepted" units="" value=1
2024-11-06T22:36:20.268297Z TRACE s2n_quic_dc::event::generated::metrics::probe::nominal_counter::replay_detected_packet_accepted__peer_address__protocol: value=1 variant=0 variant_name="IP_V4"
2024-11-06T22:36:20.268306Z TRACE s2n_quic_core::event::metrics::aggregate::probe::dynamic::nominal_counter::record: id=42 name="replay_detected_packet_accepted.peer_address.protocol" units="" variant="IP_V4" value=1
2024-11-06T22:36:20.268334Z TRACE s2n_quic_dc::event::generated::metrics::probe::counter::path_secret_map_background_handshake_requested: value=1
2024-11-06T22:36:20.268341Z TRACE s2n_quic_core::event::metrics::aggregate::probe::dynamic::counter::record: id=16 name="path_secret_map_background_handshake_requested" units="" value=1
2024-11-06T22:36:20.268351Z TRACE s2n_quic_dc::event::generated::metrics::probe::nominal_counter::path_secret_map_background_handshake_requested__peer_address__protocol: value=1 variant=0 variant_name="IP_V4"
2024-11-06T22:36:20.268359Z TRACE s2n_quic_core::event::metrics::aggregate::probe::dynamic::nominal_counter::record: id=17 name="path_secret_map_background_handshake_requested.peer_address.protocol" units="" variant="IP_V4" value=1

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.