eltype for @map result can be a "malformed" NamedTuple type

julia> coll = (row for row in [(a=1, b=Dict{Any,Any}(:c=>1))]) |> @map({_.a, c=_.b[:c]})
1-element query result
 (a = 1, c = 1)

julia> typeof(coll)
QueryOperators.EnumerableMap{NamedTuple{(:a, :c),_A} where _A,QueryOperators.EnumerableIterable{NamedTuple{(:a, :b),Tuple{Int64,Dict{Any,Any}}},IterableTables.GeneratorWithElType{NamedTuple{(:a, :b),Tuple{Int64,Dict{Any,Any}}},Base.Generator{Array{NamedTuple{(:a, :b),Tuple{Int64,Dict{Any,Any}}},1},getfield(Main, Symbol("##51#54"))}}},getfield(Main, Symbol("##53#56"))}

julia> eltype(coll)
NamedTuple{(:a, :c),_A} where _A

julia> eltype(coll) <: NamedTuple
false

Note that this breaks isiterabletable without https://github.com/queryverse/TableTraits.jl/pull/11

(v1.2) pkg> st -m Query
    Status `~/.julia/environments/v1.2/Manifest.toml`
  [e7dc6d0d] DataValues v0.4.12
  [1c8ee90f] IterableTables v0.11.0
  [1914dd2f] MacroTools v0.5.1
  [1a8c2f83] Query v0.12.2
  [2aef5ad7] QueryOperators v0.9.1
  [10745b16] Statistics

Start by reproducing the Julia example with @map and inspecting the resulting eltype; then trace how that type is produced and how it affects isiterabletable, including the referenced TableTraits change. Done means the @map result exposes a valid NamedTuple subtype and no longer breaks isiterabletable.