feat(dbmanager): ✨ add support for existing SQL connections

* Introduced NewConnectionFromDB function to create connections from existing *sql.DB instances.
* Added ExistingDBProvider to wrap existing database connections for dbmanager features.
* Implemented tests for NewConnectionFromDB and ExistingDBProvider functionalities.

pkg/dbmanager/providers/existing_db_test.go

@@ -0,0 +1,194 @@
+package providers
+
+import (
+	"context"
+	"database/sql"
+	"testing"
+	"time"
+
+	_ "github.com/mattn/go-sqlite3"
+)
+
+func TestNewExistingDBProvider(t *testing.T) {
+	// Open a SQLite in-memory database
+	db, err := sql.Open("sqlite3", ":memory:")
+	if err != nil {
+		t.Fatalf("Failed to open database: %v", err)
+	}
+	defer db.Close()
+
+	// Create provider
+	provider := NewExistingDBProvider(db, "test-db")
+	if provider == nil {
+		t.Fatal("Expected provider to be created")
+	}
+
+	if provider.name != "test-db" {
+		t.Errorf("Expected name 'test-db', got '%s'", provider.name)
+	}
+}
+
+func TestExistingDBProvider_Connect(t *testing.T) {
+	db, err := sql.Open("sqlite3", ":memory:")
+	if err != nil {
+		t.Fatalf("Failed to open database: %v", err)
+	}
+	defer db.Close()
+
+	provider := NewExistingDBProvider(db, "test-db")
+	ctx := context.Background()
+
+	// Connect should verify the connection works
+	err = provider.Connect(ctx, nil)
+	if err != nil {
+		t.Errorf("Expected Connect to succeed, got error: %v", err)
+	}
+}
+
+func TestExistingDBProvider_Connect_NilDB(t *testing.T) {
+	provider := NewExistingDBProvider(nil, "test-db")
+	ctx := context.Background()
+
+	err := provider.Connect(ctx, nil)
+	if err == nil {
+		t.Error("Expected Connect to fail with nil database")
+	}
+}
+
+func TestExistingDBProvider_GetNative(t *testing.T) {
+	db, err := sql.Open("sqlite3", ":memory:")
+	if err != nil {
+		t.Fatalf("Failed to open database: %v", err)
+	}
+	defer db.Close()
+
+	provider := NewExistingDBProvider(db, "test-db")
+
+	nativeDB, err := provider.GetNative()
+	if err != nil {
+		t.Errorf("Expected GetNative to succeed, got error: %v", err)
+	}
+
+	if nativeDB != db {
+		t.Error("Expected GetNative to return the same database instance")
+	}
+}
+
+func TestExistingDBProvider_GetNative_NilDB(t *testing.T) {
+	provider := NewExistingDBProvider(nil, "test-db")
+
+	_, err := provider.GetNative()
+	if err == nil {
+		t.Error("Expected GetNative to fail with nil database")
+	}
+}
+
+func TestExistingDBProvider_HealthCheck(t *testing.T) {
+	db, err := sql.Open("sqlite3", ":memory:")
+	if err != nil {
+		t.Fatalf("Failed to open database: %v", err)
+	}
+	defer db.Close()
+
+	provider := NewExistingDBProvider(db, "test-db")
+	ctx := context.Background()
+
+	err = provider.HealthCheck(ctx)
+	if err != nil {
+		t.Errorf("Expected HealthCheck to succeed, got error: %v", err)
+	}
+}
+
+func TestExistingDBProvider_HealthCheck_ClosedDB(t *testing.T) {
+	db, err := sql.Open("sqlite3", ":memory:")
+	if err != nil {
+		t.Fatalf("Failed to open database: %v", err)
+	}
+
+	provider := NewExistingDBProvider(db, "test-db")
+
+	// Close the database
+	db.Close()
+
+	ctx := context.Background()
+	err = provider.HealthCheck(ctx)
+	if err == nil {
+		t.Error("Expected HealthCheck to fail with closed database")
+	}
+}
+
+func TestExistingDBProvider_GetMongo(t *testing.T) {
+	db, err := sql.Open("sqlite3", ":memory:")
+	if err != nil {
+		t.Fatalf("Failed to open database: %v", err)
+	}
+	defer db.Close()
+
+	provider := NewExistingDBProvider(db, "test-db")
+
+	_, err = provider.GetMongo()
+	if err != ErrNotMongoDB {
+		t.Errorf("Expected ErrNotMongoDB, got: %v", err)
+	}
+}
+
+func TestExistingDBProvider_Stats(t *testing.T) {
+	db, err := sql.Open("sqlite3", ":memory:")
+	if err != nil {
+		t.Fatalf("Failed to open database: %v", err)
+	}
+	defer db.Close()
+
+	// Set some connection pool settings to test stats
+	db.SetMaxOpenConns(10)
+	db.SetMaxIdleConns(5)
+	db.SetConnMaxLifetime(time.Hour)
+
+	provider := NewExistingDBProvider(db, "test-db")
+
+	stats := provider.Stats()
+	if stats == nil {
+		t.Fatal("Expected stats to be returned")
+	}
+
+	if stats.Name != "test-db" {
+		t.Errorf("Expected stats.Name to be 'test-db', got '%s'", stats.Name)
+	}
+
+	if stats.Type != "sql" {
+		t.Errorf("Expected stats.Type to be 'sql', got '%s'", stats.Type)
+	}
+
+	if !stats.Connected {
+		t.Error("Expected stats.Connected to be true")
+	}
+}
+
+func TestExistingDBProvider_Close(t *testing.T) {
+	db, err := sql.Open("sqlite3", ":memory:")
+	if err != nil {
+		t.Fatalf("Failed to open database: %v", err)
+	}
+
+	provider := NewExistingDBProvider(db, "test-db")
+
+	err = provider.Close()
+	if err != nil {
+		t.Errorf("Expected Close to succeed, got error: %v", err)
+	}
+
+	// Verify the database is closed
+	err = db.Ping()
+	if err == nil {
+		t.Error("Expected database to be closed")
+	}
+}
+
+func TestExistingDBProvider_Close_NilDB(t *testing.T) {
+	provider := NewExistingDBProvider(nil, "test-db")
+
+	err := provider.Close()
+	if err != nil {
+		t.Errorf("Expected Close to succeed with nil database, got error: %v", err)
+	}
+}