Inconsistencies in `Schema`

[simsurace]

Generically, wide table schemas will bypass the type system:

Tables.jl/src/Tables.jl

Lines 477 to 483 in 2cb1399

	function Schema(names, types; stored::Bool=false)
	if stored || length(names) > SCHEMA_SPECIALIZATION_THRESHOLD
	return Schema{nothing, nothing}([sym(x) for x in names], Type[T for T in types])
	else
	return Schema{Tuple(map(sym, names)), Tuple{types...}}()
	end
	end

But not for MatrixTables:

Tables.jl/src/matrix.jl

Line 40 in 2cb1399

schema(m::MatrixTables{T}) where {T} = Schema(Tuple(names(m)), NTuple{size(getfield(m, :matrix), 2), eltype(T)})

Maybe the branch should be put in the constructor, such that it is done for any table type?

C.f. apache/arrow-julia#415