gorums: peer configuration errors repeat the gorums: prefix #369

Problem

NewServer and NewLocalServers wrap peer configuration errors in gorums: invalid peer configuration: ….
The wrapped errors already start with gorums: , so the message repeats the prefix:

gorums: invalid peer configuration: gorums: node 1 has an empty TLS identity
gorums: invalid peer configuration: gorums: missing required node map

• NewServer (server.go) panics with fmt.Sprintf("gorums: invalid peer configuration: %v", err).
• NewLocalServers (local_servers.go) returns fmt.Errorf("gorums: invalid peer configuration: %w", err).
• The wrapped errors come from conn.NewInboundManager, the node sources (WithNodes, WithNodeList), and, with gorums: authenticate peers using node TLS identities #359, the TLS identity validation.
• master has the same double prefix for the NewInboundManager and node source errors.
• With gorums: authenticate peers using node TLS identities #359, TestServerIdentityConfiguration pins the doubled text.

The verifier errors in #359 do not have this problem: stream.VerificationError is the only layer that adds the prefix.

Options

1. Drop the wrapper: NewServer panics with the error itself, and NewLocalServers returns it. The inner errors already start with gorums: and name the problem.
2. Keep the wrapper and remove the prefix from the inner errors. This does not work for the node source errors, because NewConfig returns them without a wrapper.

Option 1 is the smaller change.
Done when no configuration error repeats gorums:, and the tests pin the single-prefix text.