Surface upstream rate limits from Anthropic (#16118)

This PR makes it so hitting upstream rate limits from Anthropic result
in an HTTP 429 response instead of an HTTP 500.

To do this we need to surface structured errors out of the `anthropic`
crate.

Release Notes:

- N/A

crates/language_model/src/provider/cloud.rs

@@ -4,7 +4,8 @@ use crate::{
     LanguageModelName, LanguageModelProviderId, LanguageModelProviderName,
     LanguageModelProviderState, LanguageModelRequest, RateLimiter, ZedModel,
 };
-use anyhow::{anyhow, bail, Result};
+use anthropic::AnthropicError;
+use anyhow::{anyhow, bail, Context as _, Result};
 use client::{Client, PerformCompletionParams, UserStore, EXPIRED_LLM_TOKEN_HEADER_NAME};
 use collections::BTreeMap;
 use feature_flags::{FeatureFlagAppExt, LanguageModels};
@@ -446,16 +447,23 @@ impl LanguageModel for CloudLanguageModel {
                         match body.read_line(&mut buffer).await {
                             Ok(0) => Ok(None),
                             Ok(_) => {
-                                let event: anthropic::Event = serde_json::from_str(&buffer)?;
+                                let event: anthropic::Event = serde_json::from_str(&buffer)
+                                    .context("failed to parse Anthropic event")?;
                                 Ok(Some((event, body)))
                             }
-                            Err(e) => Err(e.into()),
+                            Err(err) => Err(AnthropicError::Other(err.into())),
                         }
                     });
 
                     Ok(anthropic::extract_text_from_events(stream))
                 });
-                async move { Ok(future.await?.boxed()) }.boxed()
+                async move {
+                    Ok(future
+                        .await?
+                        .map(|result| result.map_err(|err| anyhow!(err)))
+                        .boxed())
+                }
+                .boxed()
             }
             CloudModel::OpenAi(model) => {
                 let client = self.client.clone();