## What does this PR do?
Improves support for HTTP MITM
## How was it tested?
Did some MITMing on macOS + Linux via Docker, using Proxyman and
mitmproxy. Didn't test `XTL_HTTP_PROXY` but Sol pinkie promises me that
it's correct.
## AI tool usage
How much of this PR was AI-assisted? (check one)
- [ ] **0** - No AI was used to write code
- [x] **1** - I was assisted by AI. I reviewed the finished result.
- [ ] **2** - I set the AI going and left it to it; nobody has read the
result - no review, or AI review only
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