Add `cycle-id` ranges to synthetic pox events

[zone117x]

The signer data sent to event observers only contains a list of signer_keys, which doesn't contain information like the stacker principals associated with those keys. IIUC this is because there is a many-to-many relationship between stacker principals and signer keys that is difficult/fuzzy to calculate for the event data.

This requires event observers (like the Stacks Blockchain API) to match the signer key event data against historical synthetic pox events in order to determine the mapping of signers and associated stacking data like principals, delegation, etc.

Adding a start-cycle-id and end-cycle-id to the synthetic pox events would make logic in the event observer this much easier.