fix(decimal): honor precision/scale in YdbTypeMappingSource

Author: LiamHamsters

src/EFCore.Ydb/CHANGELOG.md

@@ -1,3 +1,4 @@
+- Fixed Decimal precision/scale mapping in EF provider and added functional tests.
 - Supported Guid (Uuid YDB type).
 - PrivateAssets="none" is set to flow the EF Core analyzer to users referencing this package [issue](https://github.com/aspnet/EntityFrameworkCore/pull/11350).
 

src/EFCore.Ydb/src/Storage/Internal/YdbTypeMappingSource.cs

@@ -111,7 +111,16 @@ RelationalTypeMappingSourceDependencies relationalDependencies
     };
 
     protected override RelationalTypeMapping? FindMapping(in RelationalTypeMappingInfo mappingInfo)
-        => base.FindMapping(mappingInfo) ?? FindBaseMapping(mappingInfo)?.Clone(mappingInfo);
+    {
+        if (mappingInfo.ClrType == typeof(decimal)
+            || string.Equals(mappingInfo.StoreTypeNameBase, "Decimal", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(mappingInfo.StoreTypeName, "Decimal", StringComparison.OrdinalIgnoreCase))
+        {
+            return Decimal.Clone(mappingInfo);
+        }
+
+        return base.FindMapping(mappingInfo) ?? FindBaseMapping(mappingInfo)?.Clone(mappingInfo);
+    }
 
     private static RelationalTypeMapping? FindBaseMapping(in RelationalTypeMappingInfo mappingInfo)
     {