support __array__(dtype=...) optional argument

[stevengj]

From JuliaPy/PythonPlot.jl#8:

julia> np = pyimport("numpy");

julia> y = range(-5,5,length=11)
-5.0:1.0:5.0

julia> np.asarray(y)
Python ndarray: array([-5., -4., -3., -2., -1.,  0.,  1.,  2.,  3.,  4.,  5.])

julia> np.asarray(y, dtype=np.float64)
ERROR: Python: TypeError: ArrayValue.__array__() takes 1 positional argument but 2 were given
Python stacktrace: none
Stacktrace:
 [1] pythrow()
   @ PythonCall ~/.julia/packages/PythonCall/XgP8G/src/err.jl:94
 [2] errcheck
   @ ~/.julia/packages/PythonCall/XgP8G/src/err.jl:10 [inlined]
 [3] pycallargs
   @ ~/.julia/packages/PythonCall/XgP8G/src/abstract/object.jl:154 [inlined]
 [4] pycall(f::Py, args::StepRangeLen{Float64, Base.TwicePrecision{Float64}, Base.TwicePrecision{Float64}, Int64}; kwargs::Base.Pairs{Symbol, Py, Tuple{Symbol}, NamedTuple{(:dtype,), Tuple{Py}}})
   @ PythonCall ~/.julia/packages/PythonCall/XgP8G/src/abstract/object.jl:165
 [5] #_#11
   @ ~/.julia/packages/PythonCall/XgP8G/src/Py.jl:360 [inlined]
 [6] top-level scope
   @ REPL[26]:1

It seems like you need to support the dtype optional argument in this method: https://github.com/cjdoris/PythonCall.jl/blob/b4528b71e9878c8a71b9bd48ff759b5d5b14267f/src/jlwrap/array.jl#L317-L326

[cjdoris]

Done on main.