Lock values are being copied in buffer and clients

[mochi-co]

go vet reports that lock values are being copied in clients.Inflight and circ.Buffer. Additionally, the signature for the buffer WriteTo is incorrect.

# github.com/mochi-co/mqtt/server
server/server.go:224:18: assignment copies lock value to cl.Inflight: github.com/mochi-co/mqtt/server/internal/clients.Inflight
# github.com/mochi-co/mqtt/server/internal/circ
server/internal/circ/buffer.go:77:9: return copies lock value: github.com/mochi-co/mqtt/server/internal/circ.Buffer contains sync.RWMutex
server/internal/circ/reader.go:18:3: literal copies lock value from b: github.com/mochi-co/mqtt/server/internal/circ.Buffer contains sync.RWMutex
server/internal/circ/reader.go:28:3: literal copies lock value from b: github.com/mochi-co/mqtt/server/internal/circ.Buffer contains sync.RWMutex
server/internal/circ/writer.go:19:3: literal copies lock value from b: github.com/mochi-co/mqtt/server/internal/circ.Buffer contains sync.RWMutex
server/internal/circ/writer.go:29:3: literal copies lock value from b: github.com/mochi-co/mqtt/server/internal/circ.Buffer contains sync.RWMutex
server/internal/circ/pool_test.go:11:20: call of require.NotNil copies lock value: sync.Pool contains sync.noCopy
server/internal/circ/writer.go:34:18: method WriteTo(w io.Writer) (total int, err error) should have signature WriteTo(io.Writer) (int64, error)

The above issues should be corrected.