Strongify wire header serialization

[hug-dev]

As we use bincode through the serialize and deserialize functions, the default is little endian and fixed int encoding. The fixed int encoding does what we want in terms of layout for integers:

Fixed size integers are encoded directly

To make sure of that, we have one test where the expected serialised representation of a request (so including the header) is written as a Vec and we parse it. If the bincode representation changes over time, this test will fail.

bincode should be fairly stable:

The encoding format is stable across minor revisions, provided the same configuration is used. This should ensure that later versions can still read data produced by a previous versions of the library if no major version change has occured.

Two improvements should be made however to make the wire header serialization stronger:

• use the little-endian/fixed int encoding explicitely instead of using the default
• add more tests such as the one linked, where a valid header is written by hand and we check that the serialization succeeds