Retry streaming Python and bin download errors (#15567)

When there is an error during the streaming download and unpack for
Python interpreter and bin installs, we would previously fail, causing a
lot of CI flakes on GitHub Actions.

The problem was that the error is not one of the extended IO errors we
were previously handling, but a regular reqwest error, nested below
layers of errors of other crates processing the stream, including some
IO errors. We now handle nested reqwest errors, too.

This surfaced another problem: Our manual retry loop couldn't inform the
retry middleware that it already performed the limit of retries, and
that the middleware should not retry anymore. While too many retries are
more a problem for debugging than for the user, this causes confusing
error output. To work around this, we disable the retries in the client
and handle all retry errors in our loop.

Fixes https://github.com/astral-sh/uv/issues/14171

Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>

crates/uv-python/src/installation.rs

@@ -5,10 +5,11 @@ use std::str::FromStr;
 
 use indexmap::IndexMap;
 use ref_cast::RefCast;
+use reqwest_retry::policies::ExponentialBackoff;
 use tracing::{debug, info};
 
 use uv_cache::Cache;
-use uv_client::BaseClientBuilder;
+use uv_client::{BaseClientBuilder, retries_from_env};
 use uv_pep440::{Prerelease, Version};
 use uv_platform::{Arch, Libc, Os, Platform};
 use uv_preview::Preview;
@@ -228,12 +229,17 @@ impl PythonInstallation {
         let scratch_dir = installations.scratch();
         let _lock = installations.lock().await?;
 
-        let client = client_builder.build();
+        // Python downloads are performing their own retries to catch stream errors, disable the
+        // default retries to avoid the middleware from performing uncontrolled retries.
+        let retry_policy =
+            ExponentialBackoff::builder().build_with_max_retries(retries_from_env()?);
+        let client = client_builder.clone().retries(0).build();
 
         info!("Fetching requested Python...");
         let result = download
             .fetch_with_retry(
                 &client,
+                &retry_policy,
                 installations_dir,
                 &scratch_dir,
                 false,