Go: refactor model API to accept model id (#15999)

### What problem does this PR solve?

Not not only model_name@instance_name@provider_name is acceptable, but
also model_id is acceptable.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

internal/common/format.go

@@ -16,7 +16,11 @@
 
 package common
 
-import "fmt"
+import (
+	"fmt"
+	"regexp"
+	"strings"
+)
 
 // PtrString formats a pointer value as a string for debug/log output.
 // Returns "<nil>" for nil pointers.
@@ -26,3 +30,45 @@ func PtrString[T any](p *T) string {
 	}
 	return fmt.Sprintf("%v", *p)
 }
+
+// composite model name format: model_name@instance_name@provider_name
+func IsCompositeModelName(modelName string) bool {
+	parts := strings.Split(modelName, "@")
+	if len(parts) != 3 {
+		return false
+	}
+	for _, p := range parts {
+		if p == "" {
+			return false
+		}
+	}
+	return true
+}
+
+func IsUUID(uuid string) bool {
+	// only lower case letters and numbers, length is 32
+	if len(uuid) != 32 {
+		return false
+	}
+	uuidRegex := regexp.MustCompile(`^[a-z0-9]+$`)
+	if uuidRegex.MatchString(uuid) {
+		return true
+	}
+	return false
+}
+
+// ExtractCompositeName splits a composite model name into three parts.
+// Returns (modelName, instanceName, providerName, true) on success,
+// or ("", "", "", false) if the name is not a valid composite name.
+func ExtractCompositeName(modelName string) (string, string, string, error) {
+	parts := strings.Split(modelName, "@")
+	if len(parts) != 3 {
+		return "", "", "", fmt.Errorf("invalid model name format")
+	}
+	for _, p := range parts {
+		if p == "" {
+			return "", "", "", fmt.Errorf("invalid model name format")
+		}
+	}
+	return parts[0], parts[1], parts[2], nil
+}