Consider providing example wireshark implementation

[bbannier]

We should consider adding an example use of Spicy to generate a Wireshark dissector.

We currently have a very rough draft on a branch in the repo, see #505.

The eventual example should likely come with

• proper CI coverage (likely: requires check for optional Wireshark dev and runtime dependencies; tests could be implemented e.g., using tshark)
• a better designed Wireshark glue layer to customize printing, and what information to expose.