feat: guard sync-over-async bridge for WASM compatibility

[MarcelRoozekrans]

Summary

• Sync methods on abstract base classes now check OperatingSystem.IsBrowser() before calling .GetAwaiter().GetResult()
• On WASM/browser: throws PlatformNotSupportedException with a message pointing to the async counterpart
• On server/.NET: sync bridge continues to work as before
• No breaking change for server-side consumers

How it works

A shared SyncBridge.ThrowIfBrowser() guard is called at the top of every sync method:

public void Open()
{
    SyncBridge.ThrowIfBrowser(nameof(OpenAsync));
    OpenCoreAsync(CancellationToken.None).GetAwaiter().GetResult();
}

What's guarded

Class	Sync methods
AsyncDbConnection	Open(), Close(), BeginTransaction(), ChangeDatabase(), Dispose()
AsyncDbCommand	ExecuteReader(), ExecuteNonQuery(), ExecuteScalar(), Prepare()
AsyncDbDataReader	Read(), NextResult(), Close(), Dispose()
AsyncDbTransaction	Commit(), Rollback(), Dispose()
AsyncDataAdapter	Fill(), Update()

Not affected

Adapter classes (AdapterDbConnection, etc.) override sync methods with direct delegation to the inner provider's native sync implementation.

Test plan

• All 216 tests pass (sync bridge still works on non-WASM)
• No test changes needed — original sync tests pass as before

🤖 Generated with Claude Code