Add number of stackers to /pox/cycles/{cycle_number} endpoint

[BLuEScioN]

Slack context: https://hiropbc.slack.com/archives/C03UFUA5Q65/p1713303894476729

I am trying to build this UI. From inspecting the new api endpoints, it seems the data available looks like this:
{
"signing_key": "0x0343b909be3379621d5e68a883e6c74c2222666f4bf6cc38fade2c9d1c57d92213",
"weight": 2,
"stacked_amount": "3286590000000000",
"weight_percent": 66.66666666666666,
"stacked_amount_percent": 66.66666666666667
}
This enables me to fill out some of the information in the design but not all of it. The data I am missing is:

• Signer key associated address
• Last vote slot
• The number of addresses stacking

Regarding signer key associated addresses:
From Matt:
this endpoint will give you stackers/addresses for a given signing_key /extended/v2/pox/cycles/{cycle_number}/signers/{signer_key}/stackers
https://stacks-blockchain-api.vercel.app/#tag/Proof-of-Transfer/operation/get_pox_cycle_signer_stackers

Regarding last vote slot:
It sounds like there is some confusion here. What does this mean? @andresgalante can you elaborate here?

Regarding # addresses stacking:
From Matt:
I think this might be a property we can add to the /extended/v2/pox/cycles/{cycle_number} endpoint --
@rafael
what do you think?

[andresgalante]

The last vote seems to have been taken during the design phase from Solana's dashboard https://solanabeach.io/validators, which was mentioned as a resource here.

We can remove it.