reqwest and hyper each read HTTP(S)_PROXY, ALL_PROXY and NO_PROXY from the
process on their own, so tests could not inject them and the pooled client
key ignored proxy changes. EnvironmentProxies now reads them through
Lookup with the same precedence hyper used, the resolved config carries
them (empty when the transport does not trust the env), and both the
provider clients and the media fetcher build from that one value.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>