Add to_nested_h to arrays

[Tobias-Knudsen]

This PR adds a new method, to_nested_h, to the Array class. The method allows converting an array of keys at multiple levels into a nested hash with a specified default value at its leaf nodes. It supports arrays of arbitrary depth and ensures consistent behavior, even for edge cases like empty arrays.

Motivation

Currently, Array#to_h works well for flat key-value pair conversions but doesn't support nested structures. This method addresses that gap, enabling developers to build nested hash structures in a clean and intuitive way.

Given a multi-dimensional array, to_nested_h generates a nested hash where the keys are derived from each level of the array. Leaf nodes in the resulting hash are assigned a default value, which can be customized.

Usage Examples

Single Level

[[:a, :b]].to_nested_h
# => { a: nil, b: nil }

Two Levels

[[:a, :b], [:x, :y]].to_nested_h(value: 0)
# => { a: { x: 0, y: 0 }, b: { x: 0, y: 0 } }

Multiple Levels

[[:a, :b], [:x, :y], [:m, :n]].to_nested_h(value: 'leaf')
# => {
#   a: { x: { m: 'leaf', n: 'leaf' }, y: { m: 'leaf', n: 'leaf' } },
#   b: { x: { m: 'leaf', n: 'leaf' }, y: { m: 'leaf', n: 'leaf' } }
# }

Empty Array

[].to_nested_h
# => {}