feat(parser)!: Make all selection return selector objects by default

- The strings/Texthandlers are only returned by `get`/`getall`/`extract`/`extract_first`. This makes the type checking/autocompletion experience consistent.
- Removed `css_first` and `xpath_first` since it doesn't make sense to leave them now.
- Made the type hints more accurate in multiple places.

scrapling/core/mixins.py

@@ -15,6 +15,9 @@ class SelectorsGeneration:
         """Generate a selector for the current element.
         :return: A string of the generated selector.
         """
+        if self._is_text_node(self._root):
+            return ""
+
         selectorPath = []
         target = self
         css = selection.lower() == "css"

scrapling/core/shell.py

@@ -583,7 +583,7 @@ class Convertor:
             raise ValueError(f"Unknown extraction type: {extraction_type}")
         else:
             if main_content_only:
-                page = cast(Selector, page.css_first("body")) or page
+                page = cast(Selector, page.css("body").first) or page
 
             pages = [page] if not css_selector else cast(Selectors, page.css(css_selector))
             for page in pages: