Serialization don't work with complex data types containing SymEngine expressions

[PerformanceCoder]

Hi!

It seems that SymEngine expressions can't be deserialized if they are included in complex types (arrays, structures, etc.).

To reproduce the problem, the following code should be executed:

using SymEngine, Serialization

@vars x y
expr = x + y

open("test.bin", "w") do f
    serialize(f, [expr, "Hello world"])
end

open("test.bin", "r") do f
    expr2 = deserialize(f)
    print(expr2)
end

Expected result: message containing x + y and Hello world. Actual result: EOFError: read end of file.

Interestingly, ["Hello world", expr] serializes as expected.