Serialization of empty julia containers forgets type parameters

[lgoettgens]

Describe the bug
Consider an empty vector of type Vector{Foo{Bar}}, i.e. the eltype of the vector itself has a type parameter. If I save this vector, and load it again (it does not matter if loading happens in the same session or a new one), it will be the empty vector of type Vector{Foo}.
In particular, running test_save_load_rountrip from https://github.com/oscar-system/Oscar.jl/blob/master/test/Serialization/setup_tests.jl with such a vector fails.
The same problem arises for 0x0 matrices and empty dicts instead of vectors

To Reproduce
Steps to reproduce the behavior, please provide a code snippet that triggers
the bug.

using Oscar, Test

x1 = Vector{Vector{Int}}() # empty vector
save("tmp.mrdi", x1)
x2 = load("tmp.mrdi")
@test x2 isa typeof(x1)

using JSONSchema
include("test/Serialization/setup_tests.jl")
mktempdir() do path
  test_save_load_roundtrip(path, x1) do loaded
    # nothing here
  end
end

the same problem arises for e.g.
x1 = Vector{MPolyRingElem{QQFieldElem}}()
x1 = Dict{MPolyRingElem{QQFieldElem}, Int}()
x1 = Dict{Int, MPolyRingElem{QQFieldElem}}()

For the following two empty containers, even trying to load raises a KeyError.
x1 = Matrix{QQMatrix}(undef, 0, 0) (will no longer error but still have the problem once #3980 is merged)
x1 = Dict{QQMatrix, Int}()
x1 = Dict{Int, QQMatrix}()

Expected behavior
All of the above containers should remember its eltype when saving and loading, as they already do if they contain some elements.

System (please complete the following information):

julia> Oscar.versioninfo(full=true)
OSCAR version 1.2.0-DEV - #master, bfcfee360a -- 2024-07-28 10:10:11 +0000
  combining:
    AbstractAlgebra.jl   v0.42.0
    GAP.jl               v0.10.4
    Hecke.jl             v0.33.0
    Nemo.jl              v0.46.0
    Polymake.jl          v0.11.19
    Singular.jl          v0.23.4
  building on:
    FLINT_jll               v300.100.300+0
    GAP_jll                 v400.1200.200+9
    Singular_jll            v404.0.301+0
    libpolymake_julia_jll   v0.12.0+0
    libsingular_julia_jll   v0.45.2+0
    polymake_jll            v400.1200.1+0
See `]st -m` for a full list of dependencies.