language_models: Pass up mode for completion requests through Zed (#29294)

This PR makes it so we pass up the `mode` for completion requests
through the Zed provider.

Release Notes:

- N/A

Cargo.lock

@@ -18400,9 +18400,9 @@ dependencies = [
 
 [[package]]
 name = "zed_llm_client"
-version = "0.6.1"
+version = "0.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ad17428120f5ca776dc5195e2411a282f5150a26d5536671f8943c622c31274f"
+checksum = "3c1666cd923c5eb4635f3743e69c6920d0ed71f29b26920616a5d220607df7c4"
 dependencies = [
  "anyhow",
  "serde",