Follow-up improvements on top of the shared resolver from PR #6562:
- Add platform_env_var parameter to resolve_proxy_url() so DISCORD_PROXY
takes priority over generic HTTPS_PROXY/ALL_PROXY env vars
- Add SOCKS proxy support via aiohttp_socks.ProxyConnector with rdns=True
(critical for GFW/Shadowrocket/Clash users — issue #6649)
- proxy_kwargs_for_bot() returns connector= for SOCKS, proxy= for HTTP
- proxy_kwargs_for_aiohttp() returns split (session_kw, request_kw) for
standalone aiohttp sessions
- Add proxy support to send_message_tool.py (Discord REST, Slack, SMS)
for cron job delivery behind proxies (from PR #2208)
- Add proxy support to Discord image/document downloads
- Fix duplicate import sys in base.py
6f8e426275