feat: add proxy/cookie/redirect + trace helpers + HEAD/OPTIONS

[cmilesdev]

Proxy, Cookie & Redirect Support

Adds first-class helpers for common HTTP behaviors without exposing low-level transport details.

• Proxy(url string)
• ProxyFunc(fn func(*http.Request) (*url.URL, error))
• CookieJar(jar http.CookieJar)
• Cookies(...*http.Cookie)
• Redirect(policies ...req.RedirectPolicy)

Tracing & Debugging Helpers

New, clearer helpers for request tracing and diagnostics:

• Trace() - enable tracing for a single request
• TraceAll() - enable tracing for all requests
• TraceTo(writer io.Writer) - direct trace output
• TraceWithoutBody(), TraceWithoutHeaders() - reduce noise

These replace ad-hoc or overly granular helpers with a small, composable surface.

Expanded HTTP Method Coverage

Completes the core HTTP API surface:

• Head(...)
• Options(...)
• Context-aware variants (HeadCtx, OptionsCtx)

Design Notes

• No breaking changes to existing behavior.
• Advanced controls (transport, TLS internals, protocol knobs) remain available but are intentionally not emphasized.
• The public API continues to prioritize:
  • clarity over completeness
  • composition over configuration
  • predictable defaults

This keeps httpx approachable for everyday use while still supporting advanced workflows when needed.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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