Simplify import statements (pals-project#30)

Re-export commonly used classes from submodules so callers can use
simpler import statements like `from pals import Drift` instead of `from
pals.Drift import Drift`.

Close pals-project#29.

Author: EZoni

examples/fodo.py

@@ -6,10 +6,10 @@
 # Add the parent directory to sys.path
 sys.path.append(os.path.abspath(os.path.join(os.path.dirname(__file__), "../src/")))
 
-from pals.MagneticMultipoleParameters import MagneticMultipoleParameters
-from pals.Drift import Drift
-from pals.Quadrupole import Quadrupole
-from pals.BeamLine import BeamLine
+from pals import MagneticMultipoleParameters
+from pals import Drift
+from pals import Quadrupole
+from pals import BeamLine
 
 
 def main():

src/pals/BeamLine.py

@@ -1,10 +1,10 @@
 from pydantic import ConfigDict, Field, model_validator
 from typing import Annotated, List, Literal, Union
 
-from pals.BaseElement import BaseElement
-from pals.ThickElement import ThickElement
-from pals.Drift import Drift
-from pals.Quadrupole import Quadrupole
+from .BaseElement import BaseElement
+from .ThickElement import ThickElement
+from .Drift import Drift
+from .Quadrupole import Quadrupole
 
 
 class BeamLine(BaseElement):

src/pals/__init__.py

@@ -0,0 +1,22 @@
+"""Top-level package for PALS.
+
+Re-export commonly used classes from submodules so callers can use
+simpler import statements like `from pals import Drift` instead of
+`from pals.Drift import Drift`.
+"""
+
+from .BaseElement import BaseElement
+from .BeamLine import BeamLine
+from .Drift import Drift
+from .MagneticMultipoleParameters import MagneticMultipoleParameters
+from .Quadrupole import Quadrupole
+from .ThickElement import ThickElement
+
+__all__ = [
+    "BaseElement",
+    "BeamLine",
+    "Drift",
+    "MagneticMultipoleParameters",
+    "Quadrupole",
+    "ThickElement",
+]

tests/test_schema.py

@@ -8,12 +8,12 @@
 
 from pydantic import ValidationError
 
-from pals.MagneticMultipoleParameters import MagneticMultipoleParameters
-from pals.BaseElement import BaseElement
-from pals.ThickElement import ThickElement
-from pals.Drift import Drift
-from pals.Quadrupole import Quadrupole
-from pals.BeamLine import BeamLine
+from pals import MagneticMultipoleParameters
+from pals import BaseElement
+from pals import ThickElement
+from pals import Drift
+from pals import Quadrupole
+from pals import BeamLine
 
 
 def test_BaseElement():