refactor: revert module namespace from canola back to oil

Problem: the canola rename creates unnecessary friction for users
migrating from stevearc/oil.nvim — every `require('oil')` call and
config reference must change.

Solution: revert all module paths, URL schemes, autocmd groups,
highlight groups, and filetype names back to `oil`. The repo stays
`canola.nvim` for identity; the code is a drop-in replacement.

lua/oil/layout.lua

@@ -0,0 +1,198 @@
+local M = {}
+
+---@param value number
+---@return boolean
+local function is_float(value)
+  local _, p = math.modf(value)
+  return p ~= 0
+end
+
+---@param value number
+---@param max_value number
+---@return number
+local function calc_float(value, max_value)
+  if value and is_float(value) then
+    return math.min(max_value, value * max_value)
+  else
+    return value
+  end
+end
+
+---@return integer
+M.get_editor_width = function()
+  return vim.o.columns
+end
+
+---@return integer
+M.get_editor_height = function()
+  local editor_height = vim.o.lines - vim.o.cmdheight
+  -- Subtract 1 if tabline is visible
+  if vim.o.showtabline == 2 or (vim.o.showtabline == 1 and #vim.api.nvim_list_tabpages() > 1) then
+    editor_height = editor_height - 1
+  end
+  -- Subtract 1 if statusline is visible
+  if
+    vim.o.laststatus >= 2 or (vim.o.laststatus == 1 and #vim.api.nvim_tabpage_list_wins(0) > 1)
+  then
+    editor_height = editor_height - 1
+  end
+  return editor_height
+end
+
+local function calc_list(values, max_value, aggregator, limit)
+  local ret = limit
+  if not max_value or not values then
+    return nil
+  elseif type(values) == 'table' then
+    for _, v in ipairs(values) do
+      ret = aggregator(ret, calc_float(v, max_value))
+    end
+    return ret
+  else
+    ret = aggregator(ret, calc_float(values, max_value))
+  end
+  return ret
+end
+
+local function calculate_dim(desired_size, exact_size, min_size, max_size, total_size)
+  local ret = calc_float(exact_size, total_size)
+  local min_val = calc_list(min_size, total_size, math.max, 1)
+  local max_val = calc_list(max_size, total_size, math.min, total_size)
+  if not ret then
+    if not desired_size then
+      if min_val and max_val then
+        ret = (min_val + max_val) / 2
+      else
+        ret = 80
+      end
+    else
+      ret = calc_float(desired_size, total_size)
+    end
+  end
+  if max_val then
+    ret = math.min(ret, max_val)
+  end
+  if min_val then
+    ret = math.max(ret, min_val)
+  end
+  return math.floor(ret)
+end
+
+M.calculate_width = function(desired_width, opts)
+  return calculate_dim(
+    desired_width,
+    opts.width,
+    opts.min_width,
+    opts.max_width,
+    M.get_editor_width()
+  )
+end
+
+M.calculate_height = function(desired_height, opts)
+  return calculate_dim(
+    desired_height,
+    opts.height,
+    opts.min_height,
+    opts.max_height,
+    M.get_editor_height()
+  )
+end
+
+---@class (exact) oil.WinLayout
+---@field width integer
+---@field height integer
+---@field row integer
+---@field col integer
+
+---@return vim.api.keyset.win_config
+M.get_fullscreen_win_opts = function()
+  local config = require('oil.config')
+
+  local total_width = M.get_editor_width()
+  local total_height = M.get_editor_height()
+  local width = total_width - 2 * config.float.padding
+  if config.float.border ~= 'none' then
+    width = width - 2 -- The border consumes 1 col on each side
+  end
+  if config.float.max_width > 0 then
+    local max_width = math.floor(calc_float(config.float.max_width, total_width))
+    width = math.min(width, max_width)
+  end
+  local height = total_height - 2 * config.float.padding
+  if config.float.max_height > 0 then
+    local max_height = math.floor(calc_float(config.float.max_height, total_height))
+    height = math.min(height, max_height)
+  end
+  local row = math.floor((total_height - height) / 2)
+  local col = math.floor((total_width - width) / 2) - 1 -- adjust for border width
+
+  local win_opts = {
+    relative = 'editor',
+    width = width,
+    height = height,
+    row = row,
+    col = col,
+    border = config.float.border,
+    zindex = 45,
+  }
+  return config.float.override(win_opts) or win_opts
+end
+
+---@param winid integer
+---@param direction "above"|"below"|"left"|"right"|"auto"
+---@param gap integer
+---@return oil.WinLayout root_dim New dimensions of the original window
+---@return oil.WinLayout new_dim New dimensions of the new window
+M.split_window = function(winid, direction, gap)
+  if direction == 'auto' then
+    direction = vim.o.splitright and 'right' or 'left'
+  end
+
+  local float_config = vim.api.nvim_win_get_config(winid)
+  ---@type oil.WinLayout
+  local dim_root = {
+    width = float_config.width,
+    height = float_config.height,
+    col = float_config.col,
+    row = float_config.row,
+  }
+  if vim.fn.has('nvim-0.10') == 0 then
+    -- read https://github.com/neovim/neovim/issues/24430 for more infos.
+    dim_root.col = float_config.col[vim.val_idx]
+    dim_root.row = float_config.row[vim.val_idx]
+  end
+  local dim_new = vim.deepcopy(dim_root)
+
+  if direction == 'left' or direction == 'right' then
+    dim_new.width = math.floor(float_config.width / 2) - math.ceil(gap / 2)
+    dim_root.width = dim_new.width
+  else
+    dim_new.height = math.floor(float_config.height / 2) - math.ceil(gap / 2)
+    dim_root.height = dim_new.height
+  end
+
+  if direction == 'left' then
+    dim_root.col = dim_root.col + dim_root.width + gap
+  elseif direction == 'right' then
+    dim_new.col = dim_new.col + dim_new.width + gap
+  elseif direction == 'above' then
+    dim_root.row = dim_root.row + dim_root.height + gap
+  elseif direction == 'below' then
+    dim_new.row = dim_new.row + dim_new.height + gap
+  end
+
+  return dim_root, dim_new
+end
+
+---@param desired_width integer
+---@param desired_height integer
+---@param opts table
+---@return integer width
+---@return integer height
+M.calculate_dims = function(desired_width, desired_height, opts)
+  local width = M.calculate_width(desired_width, opts)
+  local height = M.calculate_height(desired_height, opts)
+  return width, height
+end
+
+return M