port ai crate to ai2, with all tests passing

crates/ai2/src/completion.rs

@@ -0,0 +1,23 @@
+use anyhow::Result;
+use futures::{future::BoxFuture, stream::BoxStream};
+
+use crate::{auth::CredentialProvider, models::LanguageModel};
+
+pub trait CompletionRequest: Send + Sync {
+    fn data(&self) -> serde_json::Result<String>;
+}
+
+pub trait CompletionProvider: CredentialProvider {
+    fn base_model(&self) -> Box<dyn LanguageModel>;
+    fn complete(
+        &self,
+        prompt: Box<dyn CompletionRequest>,
+    ) -> BoxFuture<'static, Result<BoxStream<'static, Result<String>>>>;
+    fn box_clone(&self) -> Box<dyn CompletionProvider>;
+}
+
+impl Clone for Box<dyn CompletionProvider> {
+    fn clone(&self) -> Box<dyn CompletionProvider> {
+        self.box_clone()
+    }
+}