chore: add hrynco common library solution

- add the standalone HrynCo.Common solution and projects
- include the shared common library source and tests
- add package metadata and a repo gitignore

HrynCo.Common.Tests/BaseConfigurationCheckTests.cs

@@ -0,0 +1,50 @@
+namespace HrynCo.Common.Tests;
+
+using System.ComponentModel.DataAnnotations;
+using HrynCo.Common.HealthChecks;
+using FluentAssertions;
+using Microsoft.Extensions.Diagnostics.HealthChecks;
+using Xunit;
+
+public sealed class BaseConfigurationCheckTests
+{
+    [Fact]
+    public async Task CheckConfigurationAsync_ShouldReturnHealthyWhenOptionsAreValid()
+    {
+        var check = new FakeConfigurationCheck(new SampleOptions
+        {
+            Code = "ok"
+        }, "Sample");
+
+        HealthCheckResult result = await check.CheckConfigurationAsync(default);
+
+        result.Status.Should().Be(HealthStatus.Healthy);
+        result.Description.Should().Be("Sample configuration is valid.");
+    }
+
+    [Fact]
+    public async Task CheckConfigurationAsync_ShouldReturnUnhealthyWhenOptionsAreInvalid()
+    {
+        var check = new FakeConfigurationCheck(new SampleOptions(), "Sample");
+
+        HealthCheckResult result = await check.CheckConfigurationAsync(default);
+
+        result.Status.Should().Be(HealthStatus.Unhealthy);
+        result.Description.Should().Contain("Sample configuration invalid:");
+        result.Description.Should().Contain("The Code field is required.");
+    }
+
+    private sealed class FakeConfigurationCheck : BaseConfigurationCheck<SampleOptions>
+    {
+        public FakeConfigurationCheck(SampleOptions options, string name)
+            : base(options, name)
+        {
+        }
+    }
+
+    private sealed class SampleOptions
+    {
+        [Required]
+        public string? Code { get; set; }
+    }
+}