Add streaming JSON iteration to HTTPX responses

Normalized profile

What this task asks for

Add response iterators that incrementally parse JSON values from supported streaming media types. Add synchronous and asynchronous JSON iterators for JSON, NDJSON, and JSON text sequence media types. Validate optional charsets and otherwise detect UTF-8, UTF-16, or UTF-32 encodings including a UTF-8 BOM. Parse exactly one JSON value for standard JSON, yielding array elements individually and rejecting trailing data. Parse each non-blank NDJSON line as exactly one JSON text. Require record separators for JSON text sequences and enforce the specified empty-record and final-record behavior. Consume and close streaming responses once while keeping in-memory JSON iteration repeatable.