zeta: Extract usage information from response headers (#28999)

This PR updates the Zeta provider to extract the usage information from
the response headers, if they are present.

For now we just log the information, but we'll need to figure out where
this needs to get threaded through to in order to display it in the UI.

Release Notes:

- N/A

Cargo.lock

@@ -18361,10 +18361,11 @@ dependencies = [
 
 [[package]]
 name = "zed_llm_client"
-version = "0.5.1"
+version = "0.6.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9ee4d410dbc030c3e6e3af78fc76296f6bebe20dcb6d7d3fa24bca306fc8c1ce"
+checksum = "b91b8b05f1028157205026e525869eb860fa89bec87ea60b445efc91d05df31f"
 dependencies = [
+ "anyhow",
  "serde",
  "serde_json",
  "strum 0.27.1",