Add completions streaming support (foundation-model-stack#457)

Signed-off-by: Mateus Devino <[email protected]>

Author: mdevino

src/clients/openai.rs

@@ -363,9 +363,9 @@ impl CompletionsRequest {
         if self.model.is_empty() {
             return Err(ValidationError::Invalid("`model` must not be empty".into()));
         }
-        if self.prompt.is_empty() {
+        if !self.detectors.input.is_empty() && self.prompt.is_empty() {
             return Err(ValidationError::Invalid(
-                "`prompt` must not be empty".into(),
+                "`prompt` must not be empty when input detectors are provided".into(),
             ));
         }
         Ok(())
@@ -887,7 +887,7 @@ pub struct CompletionChoice {
 }
 
 /// Completion logprobs.
-#[derive(Debug, Clone, Deserialize, Serialize, PartialEq)]
+#[derive(Debug, Clone, Deserialize, Serialize, PartialEq, Default)]
 pub struct CompletionLogprobs {
     /// Tokens generated by the model.
     pub tokens: Vec<String>,