feat: add port ids

[imrishabh18]

Closes - https://github.com/tscircuit/tscircuit/issues/291

[imrishabh18]

So, only the first and last endpoint will be having start_pcb_port_id and no end_pcb_port_id, while the other will be having both, right?

[seveibar]

No the others will have undefined. It's kind of confusing and likely to change but you should only have an idea if the x y position represents the port

[imrishabh18]

This is what you mean't, that the first one is having it's port_id as the starting point and similarly the last one is having it's port_id as the starting point (bi-directional)