deepxde: defer import-time backend banner

`import deepxde` prints a multi-line backend banner ("Using backend:
pytorch ...") on first load. The eager `from .deepxde_integration
import DeepXDEAdapter` in `epde/integrate/__init__.py` and the
top-level import in `fitness.py` meant any `import epde` triggered
that banner even when no DeepXDE solver is in use (e.g. the legacy
L2 / L2LR fitness paths).

Drop the eager imports; expose `DeepXDEAdapter` via a PEP 562
`__getattr__` on `epde.integrate` so the name still resolves on first
access, but the banner only fires when DeepXDE is actually requested
(via `DeepXDEBasedFitness.apply()`'s existing lazy import at line
436).

Author: Gromwud

epde/integrate/__init__.py

@@ -2,4 +2,14 @@
 from .bop import BOPElement, BoundaryConditions
 from .pinn_integration import SolverAdapter
 from .numeric_integration import OdeintAdapter
-from .deepxde_integration import DeepXDEAdapter
+
+
+# ``deepxde_integration`` does ``import deepxde``, which prints a backend
+# banner on first load. Defer that until the DeepXDE adapter is actually
+# requested so plain ``import epde`` / ``from epde.integrate import
+# SolverAdapter`` stays quiet.
+def __getattr__(name):
+    if name == 'DeepXDEAdapter':
+        from .deepxde_integration import DeepXDEAdapter
+        return DeepXDEAdapter
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")

epde/operators/common/fitness.py

@@ -13,7 +13,10 @@
 import matplotlib.pyplot as plt
 from matplotlib import cm
 
-from epde.integrate import SolverAdapter, DeepXDEAdapter
+from epde.integrate import SolverAdapter
+# DeepXDEAdapter is imported lazily inside DeepXDEBasedFitness.apply() to
+# avoid triggering deepxde's import-time backend banner when no DeepXDE
+# solver is used (e.g. legacy L2/L2LR fitness paths).
 from epde.structure.main_structures import SoEq, Equation
 from epde.operators.utils.template import CompoundOperator
 import epde.globals as global_var