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.go

@@ -0,0 +1,111 @@
+package providers
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"sync"
+
+	"go.mongodb.org/mongo-driver/mongo"
+)
+
+// ExistingDBProvider wraps an existing *sql.DB connection
+// This allows using dbmanager features with a database connection
+// that was opened outside of the dbmanager package
+type ExistingDBProvider struct {
+	db   *sql.DB
+	name string
+	mu   sync.RWMutex
+}
+
+// NewExistingDBProvider creates a new provider wrapping an existing *sql.DB
+func NewExistingDBProvider(db *sql.DB, name string) *ExistingDBProvider {
+	return &ExistingDBProvider{
+		db:   db,
+		name: name,
+	}
+}
+
+// Connect verifies the existing database connection is valid
+// It does NOT create a new connection, but ensures the existing one works
+func (p *ExistingDBProvider) Connect(ctx context.Context, cfg ConnectionConfig) error {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	if p.db == nil {
+		return fmt.Errorf("database connection is nil")
+	}
+
+	// Verify the connection works
+	if err := p.db.PingContext(ctx); err != nil {
+		return fmt.Errorf("failed to ping existing database: %w", err)
+	}
+
+	return nil
+}
+
+// Close closes the underlying database connection
+func (p *ExistingDBProvider) Close() error {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	if p.db == nil {
+		return nil
+	}
+
+	return p.db.Close()
+}
+
+// HealthCheck verifies the connection is alive
+func (p *ExistingDBProvider) HealthCheck(ctx context.Context) error {
+	p.mu.RLock()
+	defer p.mu.RUnlock()
+
+	if p.db == nil {
+		return fmt.Errorf("database connection is nil")
+	}
+
+	return p.db.PingContext(ctx)
+}
+
+// GetNative returns the wrapped *sql.DB
+func (p *ExistingDBProvider) GetNative() (*sql.DB, error) {
+	p.mu.RLock()
+	defer p.mu.RUnlock()
+
+	if p.db == nil {
+		return nil, fmt.Errorf("database connection is nil")
+	}
+
+	return p.db, nil
+}
+
+// GetMongo returns an error since this is a SQL database
+func (p *ExistingDBProvider) GetMongo() (*mongo.Client, error) {
+	return nil, ErrNotMongoDB
+}
+
+// Stats returns connection statistics
+func (p *ExistingDBProvider) Stats() *ConnectionStats {
+	p.mu.RLock()
+	defer p.mu.RUnlock()
+
+	stats := &ConnectionStats{
+		Name:      p.name,
+		Type:      "sql", // Generic since we don't know the specific type
+		Connected: p.db != nil,
+	}
+
+	if p.db != nil {
+		dbStats := p.db.Stats()
+		stats.OpenConnections = dbStats.OpenConnections
+		stats.InUse = dbStats.InUse
+		stats.Idle = dbStats.Idle
+		stats.WaitCount = dbStats.WaitCount
+		stats.WaitDuration = dbStats.WaitDuration
+		stats.MaxIdleClosed = dbStats.MaxIdleClosed
+		stats.MaxLifetimeClosed = dbStats.MaxLifetimeClosed
+	}
+
+	return stats
+}