Move parsing http retries to EnvironmentOptions (#16284)

## Summary
- Move  parsing `UV_HTTP_RETRIES` to `EnvironmentOptions`

Relates https://github.com/astral-sh/uv/issues/14720

## Test Plan

- Tests with existing tests

crates/uv-python/src/installation.rs

@@ -5,11 +5,10 @@ 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, retries_from_env};
+use uv_client::BaseClientBuilder;
 use uv_pep440::{Prerelease, Version};
 use uv_platform::{Arch, Libc, Os, Platform};
 use uv_preview::Preview;
@@ -231,8 +230,7 @@ impl PythonInstallation {
 
         // 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 retry_policy = client_builder.retry_policy();
         let client = client_builder.clone().retries(0).build();
 
         info!("Fetching requested Python...");