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/adapters/trash/windows/powershell-connection.lua

@@ -0,0 +1,123 @@
+---@class (exact) oil.PowershellCommand
+---@field cmd string
+---@field cb fun(err?: string, output?: string)
+---@field running? boolean
+
+---@class oil.PowershellConnection
+---@field private jid integer
+---@field private execution_error? string
+---@field private commands oil.PowershellCommand[]
+---@field private stdout string[]
+---@field private is_reading_data boolean
+local PowershellConnection = {}
+
+---@param init_command? string
+---@return oil.PowershellConnection
+function PowershellConnection.new(init_command)
+  local self = setmetatable({
+    commands = {},
+    stdout = {},
+    is_reading_data = false,
+  }, { __index = PowershellConnection })
+
+  self:_init(init_command)
+
+  ---@type oil.PowershellConnection
+  return self
+end
+
+---@param init_command? string
+function PowershellConnection:_init(init_command)
+  -- For some reason beyond my understanding, at least one of the following
+  -- things requires `noshellslash` to avoid the embeded powershell process to
+  -- send only "" to the stdout (never calling the callback because
+  -- "===DONE(True)===" is never sent to stdout)
+  -- * vim.fn.jobstart
+  -- * cmd.exe
+  -- * powershell.exe
+  local saved_shellslash = vim.o.shellslash
+  vim.o.shellslash = false
+
+  -- 65001 is the UTF-8 codepage
+  -- powershell needs to be launched with the UTF-8 codepage to use it for both stdin and stdout
+  local jid = vim.fn.jobstart({
+    'cmd',
+    '/c',
+    '"chcp 65001 && powershell -NoProfile -NoLogo -ExecutionPolicy Bypass -NoExit -Command -"',
+  }, {
+    ---@param data string[]
+    on_stdout = function(_, data)
+      for _, fragment in ipairs(data) do
+        if fragment:find('===DONE%((%a+)%)===') then
+          self.is_reading_data = false
+          local output = table.concat(self.stdout, '')
+          local cb = self.commands[1].cb
+          table.remove(self.commands, 1)
+          local success = fragment:match('===DONE%((%a+)%)===')
+          if success == 'True' then
+            cb(nil, output)
+          elseif success == 'False' then
+            cb(success .. ': ' .. output, output)
+          end
+          self.stdout = {}
+          self:_consume()
+        elseif self.is_reading_data then
+          table.insert(self.stdout, fragment)
+        end
+      end
+    end,
+  })
+  vim.o.shellslash = saved_shellslash
+
+  if jid == 0 then
+    self:_set_error("passed invalid arguments to 'powershell'")
+  elseif jid == -1 then
+    self:_set_error("'powershell' is not executable")
+  else
+    self.jid = jid
+  end
+
+  if init_command then
+    table.insert(self.commands, { cmd = init_command, cb = function() end })
+    self:_consume()
+  end
+end
+
+---@param command string
+---@param cb fun(err?: string, output?: string[])
+function PowershellConnection:run(command, cb)
+  if self.execution_error then
+    cb(self.execution_error)
+  else
+    table.insert(self.commands, { cmd = command, cb = cb })
+    self:_consume()
+  end
+end
+
+function PowershellConnection:_consume()
+  if not vim.tbl_isempty(self.commands) then
+    local cmd = self.commands[1]
+    if not cmd.running then
+      cmd.running = true
+      self.is_reading_data = true
+      -- $? contains the execution status of the last command.
+      -- see https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_automatic_variables?view=powershell-7.4#section-1
+      vim.api.nvim_chan_send(self.jid, cmd.cmd .. '\nWrite-Host "===DONE($?)==="\n')
+    end
+  end
+end
+
+---@param err string
+function PowershellConnection:_set_error(err)
+  if self.execution_error then
+    return
+  end
+  self.execution_error = err
+  local commands = self.commands
+  self.commands = {}
+  for _, cmd in ipairs(commands) do
+    cmd.cb(err)
+  end
+end
+
+return PowershellConnection