Rewrite DB layer to use a Dapper provider abstraction (MySQL + SQLite)

[Ravid-A]

Summary

Rewrites the plugin's database layer to use a provider abstraction over Dapper, with swappable MySQL/MariaDB and SQLite backends selected via config, and replaces the old callback/MySqlDataReader API with async/await + parameterized queries.

The old Database class (static, MySQL-only, interpolated SQL passed to callback delegates) is gone. SQL injection vectors from string interpolation are eliminated.

What changed

• IDatabaseProvider + SqliteProvider / MySqlProvider — engine-specific connection creation and CREATE TABLE DDL only.
• WeaponStore — engine-agnostic async, parameterized CRUD (InitializeAsync, GetUserAsync, CreateUserAsync, SaveUserAsync) over Dapper. SQL is written as C# """ raw string literals.
• DatabaseProviderFactory — builds the provider from config; resolves relative SQLite paths against the plugin module directory.
• Config — new Provider ("mysql" default / "sqlite") and SqlitePath fields with provider-branched IsValid().
• Core / Utils — migrated to the async store with correct CounterStrikeSharp thread marshaling: SteamID/name read on the game thread, DB work on a Task.Run, results applied via Server.NextFrame. Disconnect-during-load and unauthorized-player races are guarded. Plugin unload flushes saves synchronously.
• Tests — new xUnit project (11 tests) covering the SQLite provider, WeaponStore CRUD (incl. a SQL-injection safety test), and the factory/config validation.
• CI — GitHub Actions workflow builds the plugin (Release) and runs the tests on push/PR.
• Docs — README documents the Provider/SqlitePath config with MySQL and SQLite examples.

Also included: a couple of small robustness fixes surfaced in review (skip players before Steam auth completes; accept port 65535) and an unrelated RetakeCapability.cs null-check simplification.

Behavior parity

Weapon-index clamping, insert-on-first-seen, update-on-leave, and the give_awp int↔enum round trip are all preserved.

Testing

• dotnet build RetakesAllocator.csproj -c Release → succeeds, 0 warnings.
• dotnet test → 11/11 passing.
• Not exercised in CI: live in-game behavior on a running CS2 server (requires the runtime).