fix: handle types without a namespace or assembly in reside-in checks

[iamAdarshh]

Function pointer types (Cecil FunctionPointerType) are created by DomainResolver with a null Namespace and a null Assembly. They only show up in ReferencedTypes, so Types() rules work, but any namespace/assembly predicate on Types(true) throws a NullReferenceException, as reported in #492:

Types(true).That().ResideInNamespace("System").GetObjects(architecture) // NRE on System.Private.CoreLib

This follows Option 1 from the issue, as the maintainer suggested: null-guard the helpers instead of dropping function pointers from the type set.

Changes

• TypeExtensions: ResidesInNamespace, ResidesInNamespaceMatching, ResidesInAssembly and ResidesInAssemblyMatching return false for a type without a namespace/assembly.
• TypeConditionsDefinition:
  • SimpleCondition builds the failure description eagerly, even for passing objects, so every ResideIn*/NotResideIn* condition dereferenced Namespace.FullName/Assembly.FullName. Those messages now go through two small helpers that fall back to "does not reside in a namespace" / "does not reside in an assembly".
  • The System.Reflection.Assembly overloads of ResideInAssembly/NotResideInAssembly compared with ruleType.Assembly.Equals(...). They now use the static Equals(a, b).
• Tests: FunctionPointerTests adds a class with a delegate*<int, void> field and covers the extension methods, the predicates (ResideIn*/DoNotResideIn*) and the conditions for both namespace and assembly. All of them failed with an NRE before this change.
• ArchLoaderTests.SameFullNameInMultipleAssemblies filters the shared test architecture's ReferencedTypes by type.Namespace.FullName. The new fixture puts a function pointer there, so that filter is now ?..

I also ran the exact snippet from the issue against System.Private.CoreLib. The 32 null-namespace referenced types are still present, and Types(true).That().ResideInNamespace("System") now returns results instead of throwing.

The issue only mentions the namespace helpers. I included the assembly side because function pointers have a null Assembly too, and ResideInAssembly on Types(true) fails the same way. If you'd rather keep this PR to the namespace fix, I'm happy to split it out.

dotnet build, dotnet test and mise run check pass locally.

Resolves #492

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.39%. Comparing base (dcf76a3) to head (fcefb43).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #501      +/-   ##
==========================================
+ Coverage   86.33%   86.39%   +0.05%     
==========================================
  Files         260      260              
  Lines       12496    12506      +10     
  Branches     1216     1222       +6     
==========================================
+ Hits        10789    10804      +15     
+ Misses       1372     1364       -8     
- Partials      335      338       +3     

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