feat(timezone): implement UTC and Beijing time conversion utilities and update bid handling

- Add functions to convert between UTC and Beijing time in timezone utility.
- Update BidsService to return latest update and publish dates in Beijing time.
- Modify BidCrawlerService to store publish dates in UTC format.
- Change database timezone configuration to UTC for consistency.

src/database/database.module.ts

@@ -20,7 +20,7 @@ import { ConfigModule, ConfigService } from '@nestjs/config';
         database: configService.get<string>('DATABASE_NAME', 'bidding'),
         entities: [__dirname + '/../**/*.entity{.ts,.js}'],
         synchronize: false,
-        timezone: '+08:00',
+        timezone: 'Z',
       }),
     }),
   ],