docs: add new content and images for traits and polymorphism section

- Updated SUMMARY.md to include a new subsection on Trait bounds and Polymorfismo.
- Added SVG image for Ferris expressing doubt (ferris-doubt.svg).
- Added PNG image for Ferris expressing love (ferris-love.png).
- Introduced important.svg to enhance the visual representation of important notes.
- Created trait-bounds-and-polimorfism.md to explain generics and polymorphism in Rust.
- Updated structures.md to reference traits more clearly.
- Enhanced extra.css for better styling of info sections with new images.

Author: Phosphorus-M

src/es/SUMMARY.md

@@ -21,4 +21,5 @@
     - [Organización de código](./fundamental/code-organization.md)
     - [Gestión de dependencias](./fundamental/dependency-managment.md)
 - [Conceptos nuevos](./new-concepts.md)
-    - [Traits](./new-concepts/traits.md)
+    - [Traits](./new-concepts/traits.md)
+        - [Trait bounds y Polimorfismo](./new-concepts/traits/trait-bounds-and-polimorfism.md)