refactor(types.ts): remove unnecessary declare function FallbackRender

[sukvvon]

What:

• remove unnecessay declare function FallbackRender

Why:

• declare is only necessary for external modules or global scope.
  • using declare for internally used functions or types is unnecessary.
  • if the function is not provided externally, it is clearer to define it explicitly.
• improved code consistency and readability.
  • by removing unnecessary declare keywords, the code becomes more concise and maintains a consistent structure.
  • directly defining function types reduces confusion between implementation and declaration.

How:

• ensuring consistency between types and implementation.
  • by removing declare and managing type definitions alongside implementations, it prevents inconsistencies between types and actual behavior.
  • code changes ensure that type definitions and implementations are updated together, enhancing maintainability.

Checklist:

• Documentation
• Tests
• Ready to be merged