Avoid panics by removing unwraps during HttpPeer and HttpHealthCheck initialization

[rxdiscovery]

Hello,

Summary

I would like to propose an improvement to enhance the stability of Pingora's upstream peer and health check modules by removing potential runtime panics during initialization.

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The Problem

Several constructors in the codebase rely on .unwrap(), which can cause a worker process to panic unexpectedly at runtime if an error occurs:

1. HttpPeer:

   • HttpPeer::new() and HttpPeer::new_mtls() call .unwrap() on the result of to_socket_addrs() and on the subsequent iterator (.next()). If DNS resolution fails or returns no addresses, the process panics.

2. HttpHealthCheck:

   • HttpHealthCheck::new() and HttpHealthCheck::new_custom() use .unwrap() during request header construction (RequestHeader::build) and peer template initialization.

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Proposed Solution

• Refactor these initializers to safely propagate errors using the ? operator instead of panicking.
• Change the return signature of HttpPeer::new, HttpPeer::new_mtls, HttpHealthCheck::new, and HttpHealthCheck::new_custom to return Result<Self> instead of Self.
• Update the associated test suites to handle the new Result returns properly.

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I have prepared a Pull Request containing these modifications and updated the relevant tests to ensure the codebase remains stable and compiles cleanly.

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Pingora info

Pingora version: 0.8.1

Steps to reproduce

A panic occurs if the DNS server is unreachable.