Add Fock distribution bar chart visualization

[Aniket-umass]

Fock distribution bar chart visualization

Adds a fockdistributionplot recipe to the Makie extension, visualizing the
Fock-state (number-state) occupation probabilities P(n) of a quantum state as a
bar chart. This mirrors QuTiP's plot_fock_distribution and complements the
existing Bloch sphere (spin) and Wigner (phase-space) plotters, extending
visualization coverage to the Fock basis.

What it does

• For a Ket, plots P(n) = |⟨n|ψ⟩|².
• For a density operator, plots the diagonal P(n) = ⟨n|ρ|n⟩.
• Default styling matches QuTiP: translucent green bars, y-axis fixed to [0, 1]
  (toggle with unit_y_range=false), x = "Fock number", y = "Occupation probability".

API

• fockdistributionplot(state; kwargs...) / fockdistributionplot!(ax, state; kwargs...)
• fockdistributionplot_axis([ax,] state; kwargs...) -> (Figure, Axis, Plot)
• Attributes: color, alpha, width; axis kwarg: unit_y_range.

When no Makie backend is loaded, calling these gives a normal MethodError
with a hint to load one (via Base.Experimental.register_error_hint).

Tests

test/test_fock_plotting.jl (tag :plotting) covers return types, rendering of
coherent / number / thermal states, custom attributes, the unit_y_range
toggle, and Observable reactivity.

Notes

• No Project.toml changes — reuses the Makie weakdep/extension already in place.

Example:-

[Krastanov]

I would stick to Makie defaults here, especially color

[Aniket-umass]

Hello Stefan,
WeakDepHelpers forces julia version 1.12, hence using it would mean the 1.10 jobs in the CI workflow will go red.

[Krastanov]

You can proceed with adding support for julia 1.10 to WeakDepHelpers

[Aniket-umass]

I have added the support for WeakDepHelpers. Once that PR is merged, the failed tests will pass.