Refactor API handlers to implement retry mechanism with configurable limits and improved error handling

- Introduced retry counter with a configurable ` RequestRetry ` limit in all handlers.
- Enhanced error handling with specific HTTP status codes for switching clients.
- Standardized response forwarding for non-retriable errors.
- Improved logging for quota and client switch scenarios.

internal/config/config.go

@@ -37,6 +37,9 @@ type Config struct {
 	// RequestLog enables or disables detailed request logging functionality.
 	RequestLog bool `yaml:"request-log"`
 
+	// RequestRetry defines the retry times when the request failed.
+	RequestRetry int `yaml:"request-retry"`
+
 	ClaudeKey []ClaudeKey `yaml:"claude-api-key"`
 }