refactor: extract connection to database logic to db module

internal/db/connection.go

@@ -0,0 +1,28 @@
+package db
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+func Connect(ctx context.Context, dbURL string) (*pgxpool.Pool, error) {
+	pool, err := pgxpool.New(ctx, dbURL)
+	if err != nil {
+		return nil, fmt.Errorf("unable to connect to database: %w", err)
+	}
+
+	if err := pool.Ping(ctx); err != nil {
+		pool.Close()
+		return nil, fmt.Errorf("unable to ping database: %w", err)
+	}
+
+	return pool, nil
+}
+
+func Close(pool *pgxpool.Pool) {
+	if pool != nil {
+		pool.Close()
+	}
+}