Add single-walled nanotube creation via 2D→cylindrical folding

[Copilot]

Adds create_nanotube() to made, constructing single-walled nanotubes by folding a 2D nanoribbon into a cylinder — the same builder-chain pattern used for nanoribbons.

Approach

• Internally builds a rectangular-lattice nanoribbon (rectangular lattice is required; non-rectangular distorts the tube)
• Applies _fold_to_nanotube(): maps nanoribbon y-coordinates (width dimension) to angular position θ = 2π(y − y_min)/C, wrapping atoms onto a cylinder of radius R = C/2π
• The (z − z_center) radial offset term generalizes correctly to multilayer materials
• New lattice: a = tube axis length (unchanged), b = c = 2R + vacuum_around_tube

New module: pristine_structures/one_dimensional/nanotube/

• NanotubeConfiguration — wraps NanoribbonConfiguration + vacuum_around_tube
• NanotubeBuilder — BaseSingleBuilder subclass; _generate() delegates to NanoribbonBuilder, _post_process() applies the cylindrical fold
• create_nanotube() — convenience function (main API)

Usage

from mat3ra.made.tools.build.pristine_structures.one_dimensional.nanotube import create_nanotube

nanotube = create_nanotube(
    material=graphene,
    miller_indices_2d=(0, 1),   # (0,1) = zigzag, (1,1) = armchair
    width=4,
    length=4,
    vacuum_around_tube=10.0,    # Å of vacuum around cross-section
)