fix: support #[Type] interfaces used as output types

[michael-georgiadis]

Closes #816

Description

#[Type] on a PHP interface is documented as a supported way to declare a GraphQL interface, but if that interface is used as an output type, building the schema blows up:

Expected GraphQL type "X" to be an MutableObjectType. 
Got a TheCodingMachine\GraphQLite\Types\TypeAnnotatedInterfaceType

It only shows up once the interface has already been registered (e.g. it was referenced by name via an outputType before the full type map is built), so it tends to surface on $schema->assertValid() rather than on a narrow query.

This was happening, because getOutputTypes() calls the object-only mapClassToType() on every supported class, interfaces included. Its "already registered" branch then calls getMutableObjectType(), which throws on an interface.

Fix

When the mapped type is a MutableInterfaceType, return its generated concrete companion instead (same conversion the method already does on the non-cached path).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.71%. Comparing base (53f9d49) to head (bf2afa4).
⚠️ Report is 161 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #817      +/-   ##
============================================
- Coverage     95.72%   91.71%   -4.02%     
- Complexity     1773     2023     +250     
============================================
  Files           154      198      +44     
  Lines          4586     5432     +846     
============================================
+ Hits           4390     4982     +592     
- Misses          196      450     +254     

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[oojacoboo]

@michael-georgiadis thanks for this!