feat: v8 encryption modes (#264)

This PR adds support for the new AEAD cryptosystems advertised by Discord, AES256-GCM and XChaCha20Poly1305. These schemes will shortly become mandatory, and provider stronger integrity/authentication guarantees over the cleartext portions of any voice packet by correctly specifying additional authenticated data.

To provide smooth switchover, we've added basic negotiation over the `CryptoMode`. This ensures that any clients who are manually specifying one of the legacy modes will automatically migrate to `Aes256Gcm` when Discord cease to advertise their original preference.

Closes #246.

---------

Co-authored-by: Kyle Simpson <kyleandrew.simpson@gmail.com>

Cargo.toml

@@ -14,10 +14,13 @@ rust-version = "1.74"
 version = "0.4.3"
 
 [dependencies]
+aead = { optional = true, version = "0.5.2" }
+aes-gcm = { optional = true, version = "0.10.3" }
 async-trait = { optional = true, version = "0.1" }
 audiopus = { optional = true, version = "0.3.0-rc.0" }
 byteorder = { optional = true, version = "1" }
 bytes = { optional = true, version = "1" }
+chacha20poly1305 = { optional = true, version = "0.10.1" }
 crypto_secretbox = { optional = true, features = ["std"], version = "0.1" }
 dashmap = { optional = true, version = "5" }
 derivative = "2"
@@ -52,6 +55,7 @@ tracing-futures = "0.2"
 twilight-gateway = { default-features = false, optional = true, version = "0.15.0" }
 twilight-model = { default-features = false, optional = true, version = "0.15.0" }
 typemap_rev = { optional = true, version = "0.3" }
+typenum = { optional = true, version = "1.17.0" }
 url = { optional = true, version = "2" }
 uuid = { features = ["v4"], optional = true, version = "1" }
 
@@ -81,10 +85,13 @@ gateway = [
     "tokio?/time",
 ]
 driver = [
+    "dep:aead",
+    "dep:aes-gcm",
     "dep:async-trait",
     "dep:audiopus",
     "dep:byteorder",
     "dep:bytes",
+    "dep:chacha20poly1305",
     "dep:crypto_secretbox",
     "dep:discortp",
     "dep:flume",
@@ -107,6 +114,7 @@ driver = [
     "dep:tokio-tungstenite",
     "dep:tokio-util",
     "dep:typemap_rev",
+    "dep:typenum",
     "dep:url",
     "dep:uuid",
     "tokio?/fs",