Modify Service Event encoding to be compatible with CBOR "strict" mode

[jordanschalm]

Context

We would like to change the global CBOR Decoder to use strict mode (see #5534). This is incompatible with the current implementation of service event decoding (see discussion https://github.com/onflow/flow-go/pull/5428#discussion_r1511987247).

Change service event encoding to be compatible with CBOR strict mode. Some implementation ideas:

• Separately encode the inner specific event type as a separate encode step

type ServiceEvent struct {
  Type string
  Event []byte
}

• Keep the existing ServiceEvent type, override "strict" mode for outer decode to read the Type field, then decode the specific inner event type with "strict" mode

Definition of Done

• Service event decoding should function without errors when CBOR "strict" mode is enabled globally