Add Validation in `canoto.Marshal`

[RodrigoVillar]

Referencing #117, it's possible for canoto.Unmarshal() to fail even if canoto.Marshal() works. An example is as follows:

type Foo struct {
    Bar []byte `canoto:"bytes,1"`

    canotoData canotoData_Foo
}

anyField := canoto.AnyField{
    Name: "Bar",
    Bar: []byte{},
}

a := canoto.Any{
    Fields: []canoto.AnyField{anyField},
}

f := &Foo{}
spec := f.CanotoSpec()

b, err := canoto.Marshal(spec, a) // err == nil

bytes, err := canoto.Unmarshal(spec, b) // err != nil

Ideally, we should have that:

canoto.Unmarshal(spec, canoto.Marshal(spec, a)) // ignoring errs

Adding a verification step to canoto.Marshal() would allow for the above to be possible.