Function check_circuit_breaker 

pub fn check_circuit_breaker(
    endpoint_pattern: &str,
) -> Result<(), Box<dyn Error + Send + Sync>>

What: Check circuit breaker state before making a request.

Inputs:

• endpoint_pattern: Endpoint pattern to check circuit breaker for

Output:

• Ok(()) if request should proceed, Err with cached error if circuit is open

Errors

• Returns Err if the circuit breaker is open and cooldown period has not expired.

Details:

• Returns error immediately if circuit is Open and cooldown not expired.
• Allows request if circuit is Closed or HalfOpen.
• Automatically transitions Open → HalfOpen after cooldown period.