Move pathfinder module to pymc_extras

- Move pathfinder module from pymc_experimental to pymc_extras
- Update directory structure to match upstream repository

Author: aphc14

pymc_experimental/inference/pathfinder/__init__.py

@@ -0,0 +1,3 @@
+from pymc_extras.inference.pathfinder.pathfinder import fit_pathfinder
+
+__all__ = ["fit_pathfinder"]

pymc_extras/inference/pathfinder/__init__.py

@@ -62,10 +62,10 @@
 from rich.table import Table
 from rich.text import Text
 
-from pymc_experimental.inference.pathfinder.importance_sampling import (
+from pymc_extras.inference.pathfinder.importance_sampling import (
     importance_sampling as _importance_sampling,
 )
-from pymc_experimental.inference.pathfinder.lbfgs import (
+from pymc_extras.inference.pathfinder.lbfgs import (
     LBFGS,
     LBFGSException,
     LBFGSInitFailed,

pymc_experimental/inference/pathfinder/importance_sampling.py renamed to pymc_extras/inference/pathfinder/importance_sampling.py

@@ -62,7 +62,7 @@ def test_pathfinder(inference_backend):
 def test_bfgs_sample():
     import pytensor.tensor as pt
 
-    from pymc_experimental.inference.pathfinder.pathfinder import (
+    from pymc_extras.inference.pathfinder.pathfinder import (
         alpha_recover,
         bfgs_sample,
         inverse_hessian_factors,