Make transferFlags a multivariate function

It is not uncommon to transfer the flags from multiple fields to one target, e.g tansferFlags(field=["a", "b", "c"], target="x"). Currently we only support this by calling transferFlagsmultiple times, which might trash up the history with empty columns. This MR makestransferFlags` a function supporting the projection of flags from many to one.

saqc/core/history.py

@@ -435,9 +435,6 @@ class History:
         new._meta = copyfunc(self._meta)
         return new
 
-    def equals(self, other: History) -> bool:
-        return self._hist.equals(other._hist) and self.meta == other.meta
-
     def __copy__(self):
         return self.copy(deep=False)