feat: add BaseDbContext, non-generic IEntity, fix Entity constructor

- add non-generic IEntity with Created/Updated only
- IEntity<TId> now extends IEntity
- remove Created = DateTimeOffset.UtcNow from Entity constructor
- add BaseDbContext with ApplyTimestamps, UtcValueConverter, DeleteBehavior.Restrict
- add UnexpectedEntityStateException
- add HrynCo.Common dependency to HrynCo.DAL.EF

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

HrynCo.DAL.EF/Exceptions/UnexpectedEntityStateException.cs

@@ -0,0 +1,11 @@
+namespace HrynCo.DAL.EF.Exceptions;
+
+using Microsoft.EntityFrameworkCore;
+
+public sealed class UnexpectedEntityStateException : Exception
+{
+    public UnexpectedEntityStateException(EntityState state)
+        : base($"Unexpected entity state: {state}")
+    {
+    }
+}