Issue Description:

Decimal values retrieved from a PostgreSQL database exhibit incorrect byte order when the application runs on an s390x machine using .NET 6.0. On x64/x86 machines, the application functions correctly. The issue is observed with Npgsql version 7.0.6.

Reproducibility:

The issue can be easily reproduced using the provided Dockerfile, which includes the source code for the application. The Dockerfile creates a simple .NET application that sends a basic request to the database, highlighting the incorrect byte order for decimal values on s390x.

Steps to Reproduce:

Build and run the provided Dockerfile on an s390x machine.
Observe the returned decimal values from the database using the specified query.

Expected Behavior:

The decimal values retrieved from the database should have consistent byte order across different architectures.

Actual Behavior:

On s390x, decimal values are returned with an inverted byte order when using Npgsql version 7.0.6, while the same application running on x64/x86 machines behaves as expected.

Environment Details:

.NET Version: 6.0
PostgreSQL Version: 12
Npgsql Version: 7.0.6
Operating System: Ubuntu 22.04.3

Dockerfile:

ARG BUILDPLATFORM=linux
FROM --platform=$BUILDPLATFORM alpine:3.17.4 AS builder

RUN apk add dotnet6-sdk

WORKDIR /app

RUN echo -e "\
<Project Sdk=\"Microsoft.NET.Sdk\">\n\

  <PropertyGroup>\n\
    <OutputType>Exe</OutputType>\n\
    <TargetFramework>net6.0</TargetFramework>\n\
    <ImplicitUsings>enable</ImplicitUsings>\n\
    <Nullable>enable</Nullable>\n\
  </PropertyGroup>\n\

  <ItemGroup>\n\
    <PackageReference Include=\"Npgsql\" Version=\"7.0.6\" />\n\
  </ItemGroup>\n\

</Project>\n\
" > ./NpgSqlTest.csproj

RUN dotnet restore

RUN echo -e "\
using System; \n\
using Npgsql; \n\

string connectionString = \"Username=postgres;Password='postgres';Server=172.17.0.1;Database=postgres;\"; \n\

using NpgsqlConnection connection = new(connectionString); \n\
connection.Open(); \n\

using NpgsqlCommand command = new(\"SELECT 1::decimal\", connection); \n\
using NpgsqlDataReader reader = command.ExecuteReader(); \n\

reader.Read(); \n\
Console.Write(reader[0]); \n\
" > ./Program.cs

RUN dotnet build -c Release -o out

WORKDIR /app/out

ENTRYPOINT ["dotnet", "NpgSqlTest.dll"]

to build and run it;

docker build -t npgsqltest .
docker run --rm npgsqltest

On a x64/x86 machine it prints 1 as expected. But on a s390x it prints 4294967296.

A query as SELECT 1::int works fine on both architectures.