Refactor python algorithm import (#5657)

* Python research import improvements

- Improve start.py for research env
- Remove unrequired imports

* Centralize algorithm imports

* Add regression test GH action

* Unit test python import clean up

* Join research and main imports

* More python import clean up

* Fix failing skipped regression algorithm

Algorithm.Python/StringToSymbolImplicitConversionRegressionAlgorithm.py

@@ -1,4 +1,4 @@
-# QUANTCONNECT.COM - Democratizing Finance, Empowering Individuals.
+# QUANTCONNECT.COM - Democratizing Finance, Empowering Individuals.
 # Lean Algorithmic Trading Engine v2.0. Copyright 2014 QuantConnect Corporation.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -11,14 +11,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from clr import AddReference
-AddReference("System")
-AddReference("QuantConnect.Algorithm")
-AddReference("QuantConnect.Common")
-
-from System import *
-from QuantConnect import *
-from QuantConnect.Algorithm import *
+from AlgorithmImports import *
 
 ### <summary>
 ### Related to GH issue 4275, reproduces a failed string to symbol implicit conversion asserting the exception
@@ -42,4 +35,4 @@ class StringToSymbolImplicitConversionRegressionAlgorithm(QCAlgorithm):
             self.MarketOrder("PEPE", 1)
         except Exception as exception:
             if "This asset symbol (PEPE 0) was not found in your security list" in str(exception) and not self.Portfolio.Invested:
-                self.SetHoldings("SPY", 1)
+                self.SetHoldings("SPY", 1)