fix: support payload-shaped response types

[Kentakoong]

Summary

• add an opt-in unwrapResponseData source option for HTTP clients that already unwrap success envelopes
• keep data-only and raw response objects unchanged
• recognize response envelopes composed through nested references and allOf
• bump the package to 0.1.6

Verification

• Node 24.18.0
• pnpm verify
• 56 test files, 305 tests passed
• coverage: 96.61% statements, 89.89% branches, 99.57% functions, 96.57% lines
• git diff --check