Refactor item validation and service logic

- Consolidated item creation and update validation into a common function to reduce code duplication.
- Updated the `validate_create` and `validate_update` functions to utilize the new common validation logic.
- Introduced a new `common_validators.py` file for shared validation functions.
- Added a new `fractions.py` file to handle fraction-related logic and searches.
- Enhanced the `LineCustom` model to use an enumeration for `fraction_type`.
- Improved the `ItemService` class with methods for locking invoices and renumbering line items.
- Updated the `Sector` model to use a boolean type for the `authorized` field.
- Fixed import issues in the router by replacing the old `a24_router` with `sitar_router`.

backend/api/v1/modules/public/reference_data/sectors/models.py

@@ -1,5 +1,5 @@
 from core.database import Base
-from sqlalchemy import PrimaryKeyConstraint, SmallInteger, String
+from sqlalchemy import Boolean, PrimaryKeyConstraint, SmallInteger, String
 from sqlalchemy.orm import Mapped, mapped_column
 
 
@@ -15,9 +15,9 @@ class Sector(Base):
     description: Mapped[str] = mapped_column(
         String(150), nullable=False
     )  # descripción oficial (en español)
-    authorized: Mapped[SmallInteger] = mapped_column(
-        SmallInteger
-    )  # 1 = autorizado, 0 = no autorizado
+    authorized: Mapped[bool] = mapped_column(
+        Boolean
+    )  # True = autorizado, False = no autorizado
 
     def __repr__(self):
         return f"<Sector(key={self.key}, description={self.description}, authorized={self.authorized})>"