Random: show method for MersenneTwister: invalidation resistance

[nsajko]

Avoid using or constructing the vector with nonconcrete element type.

Should make the sysimage more resistant to method invalidation.

[topolarity]

Sounds like a good change to me - printing immediately instead of accumulating in a temporary vector seems right

[topolarity]

I think using ", " instead of sep might also be clearer, but it's a matter of taste at that point

[nsajko]

The PR prevents these method invalidations:

{   
    "method_instance": {
        "method": "join(io::IO, iterator, delim) @ Base strings/io.jl:342",
        "method_instance": "MethodInstance for join(::IOBuffer, ::Vector{Integer}, ::String)"
    },
    "children": [
        {   
            "method_instance": {
                "method": "show(io::IO, rng::Random.MersenneTwister) @ Random ~/tmp/jl/jl/nightly/share/julia/stdlib/v1.13/Random/src/RNGs.jl:143",
                "method_instance": "MethodInstance for show(::IOBuffer, ::Random.MersenneTwister)"
            },
            "children": [
                {   
                    "method_instance": {
                        "method": "print(io::IO, x) @ Base strings/io.jl:32",
                        "method_instance": "MethodInstance for print(::IOBuffer, ::Random.MersenneTwister)"
                    },
                    "children": [
                        {   
                            "method_instance": {
                                "method": "print_to_string(xs...) @ Base strings/io.jl:136",
                                "method_instance": "MethodInstance for Base.print_to_string(::String, ::Random.MersenneTwister, ::String)"
                            },
                            "children": [
                                {   
                                    "method_instance": {
                                        "method": "string(xs...) @ Base strings/io.jl:189",
                                        "method_instance": "MethodInstance for string(::String, ::Random.MersenneTwister, ::String)"
                                    },
                                    "children": [
                                        {   
                                            "method_instance": {
                                                "method": "_advance_n!(r::Random.MersenneTwister, n::Int64, work::Vector{Float64}) @ Random ~/tmp/jl/jl/nightly/share/julia/stdlib/v1.13/Random/src/RNGs.jl:783",
                                                "method_instance": "MethodInstance for Random._advance_n!(::Random.MersenneTwister, ::Int64, ::Vector{Float64})"
                                            },
                                            "children": [
                                            ]
                                        }
                                    ]
                                }
                            ]
                        }
                    ]
                }
            ]
        }
    ]
}

[topolarity]

Thanks @nsajko !