Function should_stream 

pub fn should_stream(
    policy: &StreamingPolicy,
    size_hint: &SizeHint,
    content_type: Option<&str>,
    content_length: Option<u64>,
) -> StreamingDecision

Determines how to handle a response body based on size hints and content type.

This function implements the core streaming decision logic by examining:

1. Whether streaming is enabled in the policy
2. Content-Type header (fast path for exclusions/forced caching)
3. Size hints from the body
4. Content-Length header as fallback

Arguments

• policy - The streaming policy configuration
• size_hint - Size hint from the response body
• content_type - Content-Type header value, if present
• content_length - Content-Length header value, if present

Returns

A StreamingDecision indicating how to handle the body.