ExpressionForest init does not use node_defs argument

[tdene]

ExpressionForest's init() method takes in a node_defs argument as a dictionary.

This argument is never used.

This could cause issues if a Forest class is defined for a specific operation, like addition by-a-constant-number, and tries to re-use a pre-existing Tree class while making no changes other than modifying the node_defs argument. Anything passed into the Forest's init via node_defs will go unused.

Same issue occurs for the idem argument, though this is less likely to cause issues.