Proposal: changing the Chain interface to support types

[amitaifrey]

Currently the Chain interface is defined as follows:

type Chain interface {
	// Call runs the logic of the chain and returns the output. This method should
	// not be called directly. Use rather the Call, Run or Predict functions that
	// handles the memory and other aspects of the chain.
	Call(ctx context.Context, inputs map[string]any, options ...ChainCallOption) (map[string]any, error)
	// GetMemory gets the memory of the chain.
	GetMemory() schema.Memory
	// GetInputKeys returns the input keys the chain expects.
	GetInputKeys() []string
	// GetOutputKeys returns the output keys the chain returns.
	GetOutputKeys() []string
}

The interface assumes the following:

1. The caller will call the function with the relevant InputKeys.
2. The caller will receive the result as a map[string]any.
3. By using the GetOutputKeys() function (and sometimes previous knowledge), extract the relevant result from the map[string]any.
4. Also by prior knowledge, cast that result to the relevant type for future use in the code.

I believe this interface could be changed to be more useful. I propose the following:

// Chain is the interface all chains must implement.
type Chain[T any] interface {
	// Call runs the logic of the chain and returns the output. This method should
	// not be called directly. Use rather the Call, Run or Predict functions that
	// handles the memory and other aspects of the chain.
	Call(ctx context.Context, inputs map[string]any, options ...ChainCallOption) (T, map[string]any, error)
	// GetMemory gets the memory of the chain.
	GetMemory() schema.Memory
	// GetInputKeys returns the input keys the chain expects.
	GetInputKeys() []string
}

By typing the interface, we achieve the following:

1. No need to cast the returning result - utilizing Golang's typing system.
2. No need for GetOutputKeys().
3. Less chance for bugs due to wrong casts or unexpected response types, because the code can be statically checked at compile time.
4. No need for prior knowledge on those keys or casts.

*Note that we still return a map[string]any from the Call function for returning values other than the response itself.

This would result in a breaking change for this interface, however I believe this would increase the usability of the library and would encourage more users to use it. What are your thoughts?