When HTTPS_PROXY / HTTP_PROXY / ALL_PROXY env vars are set (or macOS system proxy
is detected), pass the proxy URL explicitly via HTTPXRequest(proxy=proxy_url) instead
of relying on httpx's trust_env mechanism, which is unreliable for HTTP CONNECT
proxies (e.g. Clash / ClashMac in fake-ip mode).
Uses the shared resolve_proxy_url() from base.py (handles env vars + macOS system
proxy detection) instead of duplicating env var reading inline. Consolidates the
proxy_configured boolean into a single proxy_url = resolve_proxy_url() call that
serves as both the gate for skipping fallback-IP transport and the value passed
to HTTPXRequest.
Co-authored-by: Hermes Agent <hermes@nousresearch.com>
Salvaged from PR #8931 by MaybeRichard.
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