requests: HTTP/1.1 response bodies and max_body limit #1118

Summary

Extend the requests package with essential HTTP/1.1 client behaviour:

• Send requests as HTTP/1.1 (default), keep Connection: close
• Read response bodies with Content-Length and chunked Transfer-Encoding
• Case-insensitive response headers
• Fix relative Location in redirects (closes "requests" does not handle redirection with relative path correctly #931)
• Default max response size 32 KiB (max_body kwarg to override/disable)

Out of scope (follow-up PRs)

• TLS certificate verification (SECURITY: Requests module HTTPS - no server certificate verification. #838)
• Real stream=True / incremental body read (requests: stream parameter is noop #777)
• gzip Content-Encoding, keep-alive pool, cookies

Testing

Unix port + ESP32 with fork mip index; extend test_requests.py socket mocks.

PR will follow from branch requests-http11-essentials.