Add reference data models and seed data for incoterms, invoice types, material types, payment methods, pedimento codes, pedimento regimens, sectors, states, transport modes, transport types, and valuation methods

- Implemented SQLAlchemy models for incoterms, invoice types, material types, payment methods, pedimento codes, pedimento regimens, sectors, states, transport modes, transport types, and valuation methods.
- Added seed data for each reference data model to populate the database with initial values.
- Ensured primary key constraints and appropriate data types for each model.
- Established relationships where necessary, particularly in pedimento codes and regimens.

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

@@ -0,0 +1,20 @@
+from sqlalchemy import String, PrimaryKeyConstraint, Index
+from sqlalchemy.orm import mapped_column, Mapped
+from core.database import Base
+
+class Country(Base):
+    __tablename__ = "countries" #GPaises
+    __table_args__ = (
+        PrimaryKeyConstraint("m3_key", name="countries_pkey"),
+        Index("ak_country_ame", "ame_key", unique=True),
+        {"schema": "public"}  # opcional
+    )
+
+    m3_key: Mapped[str] = mapped_column(String(3), nullable=False)       # clave M3
+    mex_key: Mapped[str] = mapped_column(String(2), nullable=False)      # clave país México
+    ame_key: Mapped[str] = mapped_column(String(2), nullable=False)      # clave país América / regional
+    description_es: Mapped[str] = mapped_column(String(50), nullable=False)  # nombre oficial en español
+    description_en: Mapped[str] = mapped_column(String(50), nullable=False)  # nombre en inglés para UI
+
+    def __repr__(self):
+        return f"<Country(m3_key={self.m3_key}, mex_key={self.mex_key}, ame_key={self.ame_key}, description_es={self.description_es}, description_en={self.description_en})>"