Events: Break out and non-exhaust context body structs (#54)

This PR makes many of the types under `EventContext` separate `#[non_exhaustive]` structs. This makes it more feasible to add further information to connection and packet events as required in future. On this note, driver (re)connection events now include the SSRC supplied by Discord and the domain name which was connected to.

In addition, this fixes global timed events to return a list of all live tracks, and extensively details/documents events at a high level.

This was tested using `cargo make ready`.

src/events/context/data/voice.rs

@@ -0,0 +1,20 @@
+use super::*;
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+#[non_exhaustive]
+/// Opus audio packet, received from another stream (detailed in `packet`).
+/// `payload_offset` contains the true payload location within the raw packet's `payload()`,
+/// if extensions or raw packet data are required.
+/// If `audio.len() == 0`, then this packet arrived out-of-order.
+pub struct VoiceData<'a> {
+    /// Decoded audio from this packet.
+    pub audio: &'a Option<Vec<i16>>,
+    /// Raw RTP packet data.
+    ///
+    /// Includes the SSRC (i.e., sender) of this packet.
+    pub packet: &'a Rtp,
+    /// Byte index into the packet body (after headers) for where the payload begins.
+    pub payload_offset: usize,
+    /// Number of bytes at the end of the packet to discard.
+    pub payload_end_pad: usize,
+}