feat(server-framework): add Server trait, Encode/Decode, async executor, syscall wrappers, and mock arch for host testing

crates/server-framework/src/codec/mod.rs

@@ -0,0 +1,10 @@
+#[cfg(test)]
+mod tests;
+
+pub trait Encode {
+    fn encode(&self) -> [usize; 4];
+}
+
+pub trait Decode: Sized {
+    fn decode(words: [usize; 4]) -> Option<Self>;
+}