Add test for PostgreSQL SqlState 22001 max length violation (fixes #92)

Add a PostgreSQL-specific test that verifies MaxLengthExceededException
is thrown when executing raw SQL that inserts a value exceeding the
character varying column limit. This exercises the IDbCommandInterceptor
CommandFailed path for PostgreSQL error 22001
(StringDataRightTruncation).

The PostgreSQL classifier already handles SqlState 22001 via
PostgresErrorCodes.StringDataRightTruncation. This test ensures the
full interceptor pipeline works for raw SQL operations in addition
to the existing SaveChanges and ExecuteUpdate test coverage.

https://claude.ai/code/session_0147Z5VzzZpX1pUfaAapNZie

Author: claude

EntityFramework.Exceptions/Tests/PostgreSQLTests.cs

@@ -1,5 +1,7 @@
-using EntityFramework.Exceptions.PostgreSQL;
+using EntityFramework.Exceptions.Common;
+using EntityFramework.Exceptions.PostgreSQL;
 using Microsoft.EntityFrameworkCore;
+using System.Threading.Tasks;
 using Testcontainers.PostgreSql;
 using Xunit;
 
@@ -10,6 +12,19 @@ public class PostgreSQLTests : DatabaseTests, IClassFixture<PostgreSQLDemoContex
         public PostgreSQLTests(PostgreSQLDemoContextFixture fixture) : base(fixture.DemoContext, fixture.SameNameIndexesContext)
         {
         }
+
+        [Fact]
+        public async Task MaxLengthViolationThrowsMaxLengthExceededExceptionThroughRawSql()
+        {
+            var longName = new string('G', DemoContext.ProductNameMaxLength + 5);
+
+            Assert.Throws<MaxLengthExceededException>(() =>
+                DemoContext.Database.ExecuteSqlInterpolated(
+                    $"INSERT INTO \"Products\" (\"Name\") VALUES ({longName})"));
+            await Assert.ThrowsAsync<MaxLengthExceededException>(() =>
+                DemoContext.Database.ExecuteSqlInterpolatedAsync(
+                    $"INSERT INTO \"Products\" (\"Name\") VALUES ({longName})"));
+        }
     }
 
     public class PostgreSQLDemoContextFixture : DemoContextFixture<PostgreSqlContainer>