fix: don't apply Str::singular() to relation type name references

[lorenzodalaqua]

Problem

When generating TypeScript types for relations, WriteRelationship runs the related model's class name through Str::singular() before using it as a type reference. But the interface for that model is always emitted under its exact class name, with no inflection applied.

For most model names the two happen to match, so the bug is invisible. It only breaks when a class name looks plural to the inflector. Given a model named OpeningHours:

// The interface is emitted with the exact class name:
export interface OpeningHours { ... }

// But the relation reference gets singularized, pointing at a type that doesn't exist:
export interface Store {
  // ...
  opening_hours: OpeningHour[]  // TS2304: Cannot find name 'OpeningHour'
}

The generated output doesn't compile.

Fix

Remove the Str::singular() calls in WriteRelationship and use the class name as-is, so relation references always match the emitted interface names. This affects both arms of the match:

• Plural relations (HasMany, BelongsToMany, ...) when plurals is disabled: OpeningHours[] instead of OpeningHour[]
• Singular relations (BelongsTo, HasOne, ...): OpeningHours instead of OpeningHour

The Str::plural() call for the plurals = true option is untouched. That behavior is opt-in and documented. This change only fixes the default path, where the reference should be the literal class name.

Changes

• src/Actions/WriteRelationship.php: use the exact related class name in type references
• test/Tests/Feature/Actions/WriteRelationshipTest.php: test covering a plural-looking class name in both singular and plural relation arms