agent: Improve error handling and retry for zed-provided models (#33565)

* Updates to `zed_llm_client-0.8.5` which adds support for `retry_after`
when anthropic provides it.

* Distinguishes upstream provider errors and rate limits from errors
that originate from zed's servers

* Moves `LanguageModelCompletionError::BadInputJson` to
`LanguageModelCompletionEvent::ToolUseJsonParseError`. While arguably
this is an error case, the logic in thread is cleaner with this move.
There is also precedent for inclusion of errors in the event type -
`CompletionRequestStatus::Failed` is how cloud errors arrive.

* Updates `PROVIDER_ID` / `PROVIDER_NAME` constants to use proper types
instead of `&str`, since they can be constructed in a const fashion.

* Removes use of `CLIENT_SUPPORTS_EXA_WEB_SEARCH_PROVIDER_HEADER_NAME`
as the server no longer reads this header and just defaults to that
behavior.

Release notes for this is covered by #33275

Release Notes:

- N/A

---------

Co-authored-by: Richard Feldman <oss@rtfeldman.com>
Co-authored-by: Richard <richard@zed.dev>

crates/assistant_tools/src/edit_agent/evals.rs

@@ -29,6 +29,7 @@ use std::{
     path::Path,
     str::FromStr,
     sync::mpsc,
+    time::Duration,
 };
 use util::path;
 
@@ -1658,12 +1659,14 @@ async fn retry_on_rate_limit<R>(mut request: impl AsyncFnMut() -> Result<R>) ->
         match request().await {
             Ok(result) => return Ok(result),
             Err(err) => match err.downcast::<LanguageModelCompletionError>() {
-                Ok(err) => match err {
-                    LanguageModelCompletionError::RateLimitExceeded { retry_after } => {
+                Ok(err) => match &err {
+                    LanguageModelCompletionError::RateLimitExceeded { retry_after, .. }
+                    | LanguageModelCompletionError::ServerOverloaded { retry_after, .. } => {
+                        let retry_after = retry_after.unwrap_or(Duration::from_secs(5));
                         // Wait for the duration supplied, with some jitter to avoid all requests being made at the same time.
                         let jitter = retry_after.mul_f64(rand::thread_rng().gen_range(0.0..1.0));
                         eprintln!(
-                            "Attempt #{attempt}: Rate limit exceeded. Retry after {retry_after:?} + jitter of {jitter:?}"
+                            "Attempt #{attempt}: {err}. Retry after {retry_after:?} + jitter of {jitter:?}"
                         );
                         Timer::after(retry_after + jitter).await;
                         continue;