[Bug]: NullReferenceException in ResidesInNamespace when using Types(true)

[AvremelM]

Description

Namespace predicates (ResideInNamespace, ResideInNamespaceMatching) throw a NullReferenceException when the architecture includes function-pointer types, because IType.Namespace is null for them and the extension dereferences it without a guard.

Minimal Working Example

using System.Linq;
using ArchUnitNET.Loader;

var architecture = new ArchLoader()
    .LoadAssemblies(typeof(System.DateTime).Assembly)   // System.Private.CoreLib
    .Build();

// Works fine
Types().That().ResideInNamespace("System").GetObjects(architecture).Count(); 

// Throws NRE
Types(true).That().ResideInNamespace("System").GetObjects(architecture).Count();

Expected Behavior

Types with null namespaces would not match any namespace predicate.

Actual Behavior

Types with null namespaces cause a NullReferenceException

Stack

Object reference not set to an instance of an object.
   at ArchUnitNET.Domain.Extensions.NamingExtensions.FullNameEquals(IHasName cls, String fullName)
   at ArchUnitNET.Domain.Extensions.TypeExtensions.ResidesInNamespace(IType e, String fullName)
   at ArchUnitNET.Fluent.Syntax.Elements.Types.TypePredicatesDefinition`1.<>c__DisplayClass9_0.<ResideInNamespace>b__0(T type)
   at System.Linq.Enumerable.ArrayWhereIterator`1.GetCount(Boolean onlyIfCheap, ReadOnlySpan`1 source, Func`2 predicate)
   at System.Linq.Enumerable.ListWhereIterator`1.GetCount(Boolean onlyIfCheap)

ArchUnitNET Version

0.13.4

.NET Version

.NET 9 (or any CoreCLR version)

Additional Context

32 types with a null Namespace, all Cecil FunctionPointerType, e.g.
method System.Object *(System.IntPtr,System.Object)
method System.Boolean *(System.Object)
They appear only in ReferencedTypes (0 in Types).

Suggested fix:

• Option 1: Null-guard the namespace extensions, e.g. return e.Namespace?.FullNameMatches(pattern) ?? false; (same for ResidesInNamespace).
• Option 2: Skip FunctionPointerType when building the type set — ArchBuilder already filters Microsoft.CodeAnalysis.EmbeddedAttribute, System.Runtime.CompilerServices.Nullable(Context)Attribute and Coverlet*.

I'm more than happy to open a PR for either approach (or any other solution) if that helps.