[FEATURE] ScannedRNN hidden state initialisation improvement

[lbeyers]

Please describe the purpose of the feature. Is it related to a problem?

Every time a hidden state is initialised with ScannedRNN.initialise_carry, a variable giving dimension for the layer width is required (sometimes this variable is called hidden_size or actor_network.pre_torso.layer_sizes[-1]). This is particularly a problem in the evaluator, where this variable cannot be consistently named between systems.

Describe the solution you'd like

When a ScannedRNN is initialised for use in a larger network, the hidden size must be recorded in such a way that it will be available whenever the hidden state must be reinitialised. I propose solutions below in order of preference:

• When a ScannedRNN is used in a larger network, have that network optionally take in a hidden state. If no hidden state is provided, it will be automatically reinitialised.
• Potentially, redo ScannedRNN to initialise hidden state automatically when it does not receive one specifically.
• Alternatively, have an instance of the ScannedRNN live inside the greater network and have that instance retain its hidden size in a viewable way.

How do we know when implementation of this feature is complete?

Checklist:

• In the evaluator and all system files, initialise_carry has access to a hidden size variable that is directly linked to the network the carry is then used for
• OR initialise_carry is only ever called INSIDE the ScannedRNN or greater network (ie actor network or q learner network).

Additional context

This is a change that is too big to handle before the next deadline. It may affect all systems and their configs.