chore: stub out resolver which will be main entry point of the package

tests/StevanFreeborn.Atproto.IdentityResolver.Tests/ResolverTests.cs

@@ -0,0 +1,10 @@
+namespace StevanFreeborn.Atproto.IdentityResolver.Tests;
+
+public class ResolverTests
+{
+  [Fact]
+  public async Task ResolveAsync_WhenCalledWithInvalidDid_ItShouldThrowInvalidArgumentException()
+  {
+    true.Should().BeTrue();
+  }
+}