Add network configuration for v1 recipe support

[danyeaw]

Checklist

• I added a descriptive title
• I searched open requests and couldn't find a duplicate

What is the idea?

Pass networking config (auth tokens, user-agents, proxies) to py-rattler-build.

Why is this needed?

Private channels need authentication, corporate networks need proxies.

What should happen?

1. Research networking API in py-rattler-build
2. Pass through auth tokens from .condarc or env vars
3. Configure user-agent and proxy settings

Additional Context

• Auth: .condarc or CONDA_TOKEN_* env vars
• Proxies: HTTP_PROXY, HTTPS_PROXY, NO_PROXY
• May require coordinating new py-rattler-build APIs if networking details not currently exposed