fix: correctly resolve array index in nested arrays

[Nikita-90]

Problem

When the cursor is inside a deeply nested array, the array index is shown as [] instead of the actual index (e.g. [0]).

Example: with this JSON:

{
  "users": [
    {
      "orders": [
        { "id": 1 }
      ]
    }
  ]
}

With cursor on "id", the winbar shows .users[].orders[] instead of .users[0].orders[0].

Root cause

When traversing the treesitter tree upward, the original code used current_node:parent() to find which child of an array contains the cursor. This is always the direct parent of the initial cursor node, so it only matched when the array was the immediate parent. For any outer/nested array, the comparison failed and the index stayed as []. Additionally, iterating all children with ipairs counted anonymous nodes (brackets, commas), causing an off-by-one error.

Fix

For each named child of the array, walk up from current_node to check if the cursor is inside that child. This correctly handles nested arrays at any depth.

-- before
for i, child in ipairs(get_children(node)) do
  local parent = current_node:parent()
  if parent == child then
    accessor = string.format("[%d]", i - 1)
  end
end

-- after
local index = 0
for child in node:iter_children() do
  if child:named() then
    local n = current_node
    while n and n ~= node do
      if n == child then
        accessor = string.format("[%d]", index)
        break
      end
      n = n:parent()
    end
    if accessor ~= "" then break end
    index = index + 1
  end
end