Split sampling into three modules

Closes #6141

Author: michaelosthege

.github/workflows/tests.yml

@@ -59,6 +59,8 @@ jobs:
             pymc/tests/distributions/test_censored.py
             pymc/tests/distributions/test_simulator.py
             pymc/tests/distributions/test_truncated.py
+            pymc/tests/test_sampling_predictive.py
+            pymc/tests/stats/test_convergence.py
 
           - |
             pymc/tests/tuning/test_scaling.py
@@ -147,7 +149,7 @@ jobs:
         python-version: ["3.8"]
         test-subset:
           - pymc/tests/variational/test_approximations.py pymc/tests/variational/test_callbacks.py pymc/tests/variational/test_inference.py pymc/tests/variational/test_opvi.py pymc/tests/test_initial_point.py
-          - pymc/tests/test_model.py pymc/tests/step_methods/test_compound.py pymc/tests/step_methods/hmc/test_hmc.py
+          - pymc/tests/test_model.py pymc/tests/test_sampling_utils.py pymc/tests/step_methods/test_compound.py pymc/tests/step_methods/hmc/test_hmc.py
           - pymc/tests/gp/test_cov.py pymc/tests/gp/test_gp.py pymc/tests/gp/test_mean.py pymc/tests/gp/test_util.py pymc/tests/ode/test_ode.py pymc/tests/ode/test_utils.py pymc/tests/smc/test_smc.py pymc/tests/test_parallel_sampling.py
           - pymc/tests/test_sampling.py pymc/tests/step_methods/test_metropolis.py pymc/tests/step_methods/test_slicer.py pymc/tests/step_methods/hmc/test_nuts.py
 

pymc/__init__.py

@@ -68,6 +68,8 @@ def __set_compiler_flags():
 from pymc.plots import *
 from pymc.printing import *
 from pymc.sampling import *
+from pymc.sampling_predictive import *
+from pymc.sampling_utils import *
 from pymc.smc import *
 from pymc.stats import *
 from pymc.step_methods import *

pymc/sampling.py

@@ -7,7 +7,8 @@
 from typing import Any, Callable, Dict, List, Optional, Sequence, Union
 
 from pymc.initial_point import StartDict
-from pymc.sampling import RandomSeed, _get_seeds_per_chain, _init_jitter
+from pymc.sampling import _init_jitter
+from pymc.sampling_utils import RandomSeed, _get_seeds_per_chain
 
 xla_flags = os.getenv("XLA_FLAGS", "")
 xla_flags = re.sub(r"--xla_force_host_platform_device_count=.+\s", "", xla_flags).split()