fix: event filter typespec generation for events with interleaved indexed and non-indexed fields

[ricomateo]

Description

The generate_event_typespecs function calls Enum.take(selector.types, arity) to extract the types of the indexed fields from an event selector. The problem with this is that Enum.take(selector.types, arity) grabs the first arity types from the full ABI field list, but when an event has interleaved indexed and non-indexed fields, this produces wrong typespecs (the generated spec contains the type of a non-indexed field instead of the actual indexed field).

Example

Take for example the following event

event Transfer(uint256 amount, address indexed sender, bool isFinal, address indexed receiver)

The arity of this event is 2 (there are 2 indexed fields), so in this case the generate_event_typespecs function will select the first 2 fields to determine the type of the indexed fields.

As a result, the generate_event_typespecs function will return [uint256, address]. However, the types of the indexed fields are actually [address, address].

This PR fixes this error by updating the generate_event_typespecs function so that it uses the event_indexed_types function to select the types for the event typespec. This ensures the typespec is generated with the right types.

[alisinabh]

Thank you for the contribution <3