Add request/response timing breakdown

[kavix]

Description

kurl shows total request time, but doesn't break down DNS lookup, connection, TLS handshake, time to first byte, etc.

Proposed Implementation

kurl https://api.example.com --timing

Output:

Timing:
  DNS Lookup:     45ms
  TCP Connection: 30ms
  TLS Handshake:  120ms
  Server Processing: 200ms
  Content Transfer: 15ms
  Total:          410ms

Why this matters

Performance debugging requires knowing where time is spent. curl has this via --write-out, kurl should make it prettier.

Acceptance Criteria

• Add --timing flag
• Measure and display DNS, TCP, TLS, TTFB, transfer phases
• Use Go's httptrace package for accurate measurements
• Format output cleanly aligned
• Add test coverage

Getting Started

Go's net/http/httptrace package provides callbacks for each phase. Wrap the transport and collect timestamps.

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