feat: mine nonce

[nugaon]

Hello there!

I needed to mine nonce of overlay address for an already existing wallet.
I though I am going to share the code since theoretically it provides a faster overlay address mining than finding the correct private key with constant nonce.

I plugged this feat into the overlay manual-mine command and it got an additional address -a option to define the base Ethereum address. You can use it like this:

$ swarm-tools overlay manual-mine -a 0x8e3cb0148c5f39577fb815dc8c37795e30f5dcfa -n 26471 -r 16 --network-id 0

Mining overlay address for neighbourhood 26471/65535
Mined nonce: 0x0000000000000000000000000000000000000000000000000000000000003ba6
Mined overlay address: 0x676720d79d609ed462fadf6f14eb1bf9ec1a90999dd45a671d79a89c7b5ac9d8