Add WithAttributedMetadata for individual registrations

[tillig]

Closes #11.

Rebased onto develop now that #21 is merged; this PR is a single commit.

Problem

Attributed metadata could only be opted into via assembly scanning. Individual registrations had to fall back to AttributedMetadataModule, so the two registration styles behaved differently for no good reason.

Change

One new overload, so RegisterType and RegisterAssemblyTypes opt in the same way:

builder.RegisterType<CenturyArtwork>().As<IArtwork>().WithAttributedMetadata();

Design note

The natural shape - an arity-3 overload constrained to ReflectionActivatorData - does not compile. ScanningActivatorData derives from ReflectionActivatorData, and generic constraints are not part of a method signature, so it is a duplicate of the existing scanning overload and fails with CS0111. I verified this rather than assuming it.

Closing over ConcreteReflectionActivatorData/SingleRegistrationStyle instead sidesteps that, and is exactly what RegisterType<T>() and RegisterType(Type) return. There is a test asserting the scanning overload still binds unambiguously.

Scope

Covers reflection-based registrations, where the implementation type is known at registration time. Delegate registrations (Register(c => ...)) have no ImplementationType and still need the module; that limitation is documented on the method.

The open question in #11

Make sure that if both the AttributedMetadataModule and the WithAttributedMetadata extension are used that we don't have conflict issues.

No conflict. AttributedMetadataModule skips metadata keys that are already present, so metadata is applied once rather than throwing on a duplicate key. Covered by a test.

Verification

dotnet msbuild ./default.proj clean: 22/22 tests pass on net10.0 and net8.0 (17 plus 5 new), zero warnings, packages build. dotnet format --verify-no-changes is clean.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.52%. Comparing base (abb7343) to head (38d5150).

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #22      +/-   ##
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+ Coverage    54.54%   56.52%   +1.97%     
===========================================
  Files            4        4              
  Lines           66       69       +3     
  Branches        23       24       +1     
===========================================
+ Hits            36       39       +3     
  Misses          14       14              
  Partials        16       16              

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