Consider refactoring primitive type `TorrentsMetrics`

[josecelano]

The type TorrentsMetrics includes the same info as the SwarmMetadata:

torrust_tracker_primitives::swarm_metadata
pub struct SwarmMetadata {
    pub downloaded: u32,
    pub complete: u32,
    pub incomplete: u32,
}

torrust_tracker_primitives::torrent_metrics
pub struct TorrentsMetrics {
    pub complete: u64,
    pub downloaded: u64,
    pub incomplete: u64,
    pub torrents: u64,
}

We could refactor it to:

torrust_tracker_primitives::torrent_metrics
pub struct TorrentsMetrics {
    pub swarm_metadata: SwarmMetadata,
    pub torrents: u64,
}

SwarmMetadata would not change.

What do you think @da2ce7?

IMPORTANT: do not start this refactor until I finish the Overhaul core::Tracker epic.

[josecelano]

I've just realized they are different because TorrentsMetrics are for all torrents while SwarmMetadata is only for one torrent. I will only make minor changes to make than difference clearer.