feat: migrate to quick-protobuf

Instead of relying on `protoc` and buildscripts, we generate the bindings using `pb-rs` and version them within our codebase. This makes for a better IDE integration, a faster build and an easier use of `rust-libp2p` because we don't force the `protoc` dependency onto them.

Resolves #3024.

Pull-Request: #3312.

core/src/identity/error.rs

@@ -68,13 +68,6 @@ impl DecodingError {
         }
     }
 
-    pub(crate) fn unknown_key_type(key_type: i32) -> Self {
-        Self {
-            msg: format!("unknown key-type {key_type}"),
-            source: None,
-        }
-    }
-
     pub(crate) fn decoding_unsupported(key_type: &'static str) -> Self {
         Self {
             msg: format!("decoding {key_type} key from Protobuf is unsupported"),