Implement and enforce explicit re-export for cirq modules (#6722)

* Enable and enforce the `no_implicit_reexport` mypy rule for cirq modules
* Update `__init__.py` files so they explicitly re-export public symbols, but
  do not re-export local symbols or submodules already in parent namespace
* Fix few instances of imports from incorrect modules

Fixes #6717
---------

Co-authored-by: Pavol Juhas <juhas@google.com>

cirq-aqt/cirq_aqt/__init__.py

@@ -14,7 +14,9 @@
 
 """Types and methods related to the AQT ion trap device"""
 
-from cirq_aqt._version import __version__
-
-from cirq_aqt.aqt_sampler import AQTSampler, AQTSamplerLocalSimulator
-from cirq_aqt.aqt_device import AQTSimulator
+from cirq_aqt._version import __version__ as __version__
+from cirq_aqt.aqt_sampler import (
+    AQTSampler as AQTSampler,
+    AQTSamplerLocalSimulator as AQTSamplerLocalSimulator,
+)
+from cirq_aqt.aqt_device import AQTSimulator as AQTSimulator

cirq-aqt/cirq_aqt/json_test_data/__init__.py

@@ -17,4 +17,4 @@
 # cirq/protocols/json_serialization_test.py which checks for coverage of
 # public classes and tests the correctness of repr and json results
 
-from cirq_aqt.json_test_data.spec import TestSpec
+from cirq_aqt.json_test_data.spec import TestSpec as TestSpec