Add player statistics system with SQLite and MySQL support

[KotyaraDev]

What to do

Implement a statistics system that tracks player performance in Zombie Mode.

Features to track

• Number of rounds played as Human
• Number of rounds played as Zombie
• Humans killed (as Zombie)
• Zombies killed (as Human)
• Times infected
• Total damage dealt
• Wins as Human / Wins as Zombie
• Longest survival time as last human

Technical requirements

• Support both SQLite (default, file-based) and MySQL (for big servers)
• Use Dapper or EF Core (choose one)
• Create core/Statistics/ or features/Statistics/ folder
• Add configuration options in SimpleZombieMode.json:
  • EnableStatistics (bool)
  • DatabaseType ("SQLite" or "MySQL")
  • ConnectionString
• Statistics should be saved at the end of each round
• Add simple commands: !szm_stats and !szm_top (top 10 players)

Acceptance criteria

• Database is created automatically on first load
• No performance impact when statistics are disabled
• Clean architecture (repository pattern recommended)
• All data is saved correctly after round ends