Tighten type of gas estimator

Author: cburgdorf

eth/estimators/__init__.py

@@ -1,14 +1,20 @@
 import os
 from typing import (
-    Any,
+    Callable,
 )
 
+from eth.rlp.transactions import (
+    BaseTransaction,
+)
 from eth.utils.module_loading import (
     import_string,
 )
+from eth.vm.state import (
+    BaseState,
+)
 
 
-def get_gas_estimator() -> Any:
+def get_gas_estimator() -> Callable[[BaseState, BaseTransaction], int]:
     import_path = os.environ.get(
         'GAS_ESTIMATOR_BACKEND_FUNC',
         'eth.estimators.gas.binary_gas_search_intrinsic_tolerance',