Auto-parse additional response content types

[zoedsoupe]

Problem

JS auto-parses multiple content types. Elixir only auto-parses JSON.

JS Parsing:

• application/json → JSON ✅ (Elixir has)
• application/octet-stream → Blob ❌
• text/event-stream → Stream ❌
• multipart/form-data → FormData ❌

Proposed Solution

Auto-parse based on Content-Type header for common formats.

Benefits

• Less boilerplate
• Better DX
• Feature parity with JS

JS Reference: functions-js/src/helper.ts:1-14