Add methods for unimplimented Neynar V2 endpoints

[piratekev]

Describe the solution you'd like
The latest Neynar V2 spec includes the following new endpoints:

GET /farcaster/user/bulk
POST & DELETE /farcaster/user/verification
GET /farcaster/user/custody-address
GET /farcaster/notifications
GET /farcaster/followers/relevant

Implement methods to expose the functionality of these endpoints. The following methods should be implemented in the Neynar V2 client and have tests added:

getUsers(fids: string[])
addVerification(signerUuid: string, address: string, blockHash: string, ethSignature: string)
deleteVerification(signerUuid: string, address: string, blockHash: string, ethSignature: string)
getUserByVerificationAddress(address: string)
getUserNotifications(fid: string)
getUserRelevantFollowers(targetFid: string, viewerFid: string)

Additional context
For the new verification methods, it's worth looking into abstracting away signing the message from the user, similar to what's done in the hub-rest package for signing verifications.

The Neynar V2 spec can be found here: neynarxyz/OAS/blob/main/src/v2/spec.yaml.

There are some manual steps to clean up the spec so that it works for us:

1. Delete the Parameter ApiKey everywhere it occurs
2. Replace the security and securitySchemes blocks in the swagger. The first 20 lines of the file should look like this:

openapi: 3.0.0
info:
  title: Farcaster API V2
  version: "2.0"
servers:
  - url: https://api.neynar.com/v2
security:
  - ApiKeyAuth: []

components:
  securitySchemes:
    ApiKeyAuth:
      type: apiKey
      in: header
      name: api_key
      description: API key required for authentication. use value --> NEYNAR_API_DOCS<-- for testing
  schemas: