feat(client): native HTTP/1.1 client replacing may_http

[casibbald]

Add feature-gated may_minihttp::client with HttpClient, Request, and Response API-compatible with may_http::client. DELETE/PUT/PATCH write_head is safe (no Drop panic). Enables BRRTRouter to drop the abandoned may_http crate without waiting on upstream.

[gemini-code-assist]

Code Review

This pull request introduces a native, feature-gated HTTP/1.1 client module (client) to may_minihttp, eliminating the dependency on the abandoned may_http crate. The implementation includes connection management via HttpClient, buffered I/O handling with BufferIo, request and response body streaming using BodyReader and BodyWriter, and outgoing/incoming message models (Request and Response). Additionally, comprehensive documentation, design documents, and epic stories are added to guide the development and integration. As there are no review comments provided, I have no further feedback to offer.

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