Add PostgreSQL provider and EF Core 10 support

Introduce Jellyfin.Database.Providers.Postgres project, enabling PostgreSQL as a database backend using Entity Framework Core 10 and Npgsql. Add custom value converters and model builder extensions for PostgreSQL compatibility. Update solution-wide dependencies to Microsoft.EntityFrameworkCore 10.0.3 and Npgsql.EntityFrameworkCore.PostgreSQL 9.0.2 (as a temporary workaround until 10.x is released). Regenerate all relevant NuGet, build, and cache files. Add new and updated binaries, debug symbols, and XML documentation for affected projects. No application source code changes outside of the new provider and supporting infrastructure.

src/Jellyfin.Database/Jellyfin.Database.Providers.Postgres/ModelBuilderExtensions.cs

@@ -0,0 +1,51 @@
+// <copyright file="ModelBuilderExtensions.cs" company="PlaceholderCompany">
+// Copyright (c) PlaceholderCompany. All rights reserved.
+// </copyright>
+
+namespace Jellyfin.Database.Providers.Postgres;
+
+using System;
+using Jellyfin.Database.Providers.Postgres.ValueConverters;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
+
+/// <summary>
+/// Model builder extensions for PostgreSQL.
+/// </summary>
+public static class ModelBuilderExtensions
+{
+    /// <summary>
+    /// Specify value converter for the object type.
+    /// </summary>
+    /// <param name="modelBuilder">The model builder.</param>
+    /// <param name="converter">The <see cref="ValueConverter{TModel,TProvider}"/>.</param>
+    /// <typeparam name="T">The type to convert.</typeparam>
+    /// <returns>The modified <see cref="ModelBuilder"/>.</returns>
+    public static ModelBuilder UseValueConverterForType<T>(this ModelBuilder modelBuilder, ValueConverter converter)
+    {
+        var type = typeof(T);
+        foreach (var entityType in modelBuilder.Model.GetEntityTypes())
+        {
+            foreach (var property in entityType.GetProperties())
+            {
+                if (property.ClrType == type)
+                {
+                    property.SetValueConverter(converter);
+                }
+            }
+        }
+
+        return modelBuilder;
+    }
+
+    /// <summary>
+    /// Specify the default <see cref="DateTimeKind"/>.
+    /// </summary>
+    /// <param name="modelBuilder">The model builder to extend.</param>
+    /// <param name="kind">The <see cref="DateTimeKind"/> to specify.</param>
+    public static void SetDefaultDateTimeKind(this ModelBuilder modelBuilder, DateTimeKind kind)
+    {
+        modelBuilder.UseValueConverterForType<DateTime>(new DateTimeKindValueConverter(kind));
+        modelBuilder.UseValueConverterForType<DateTime?>(new DateTimeKindValueConverter(kind));
+    }
+}