executor,functests: Add tests for :luado, also some fixes

Fixes:
1. Allocate space for the NUL byte.
2. Do not exclude last line from range.
3. Remove code for sandbox: it is handled earlier.
4. Fix index in new_line_transformed when converting NULs to NLs.
5. Always allocate new_line_transformed, but save allocated value.

test/functional/lua/commands_spec.lua

@@ -63,3 +63,48 @@ describe(':lua command', function()
     eq(42, funcs.luaeval('gvar'))
   end)
 end)
+
+describe(':luado command', function()
+  it('works', function()
+    curbufmeths.set_lines(0, 1, false, {"ABC", "def", "gHi"})
+    eq('', redir_exec('luado lines = (lines or {}) lines[#lines + 1] = {linenr, line}'))
+    eq({'ABC', 'def', 'gHi'}, curbufmeths.get_lines(0, -1, false))
+    eq({{1, 'ABC'}, {2, 'def'}, {3, 'gHi'}}, funcs.luaeval('lines'))
+
+    -- Automatic transformation of numbers
+    eq('', redir_exec('luado return linenr'))
+    eq({'1', '2', '3'}, curbufmeths.get_lines(0, -1, false))
+
+    eq('', redir_exec('luado return ("<%02x>"):format(line:byte())'))
+    eq({'<31>', '<32>', '<33>'}, curbufmeths.get_lines(0, -1, false))
+  end)
+  it('stops processing lines when suddenly out of lines', function()
+    curbufmeths.set_lines(0, 1, false, {"ABC", "def", "gHi"})
+    eq('', redir_exec('2,$luado runs = ((runs or 0) + 1) vim.api.nvim_command("%d")'))
+    eq({''}, curbufmeths.get_lines(0, -1, false))
+    eq(1, funcs.luaeval('runs'))
+  end)
+  it('works correctly when changing lines out of range', function()
+    curbufmeths.set_lines(0, 1, false, {"ABC", "def", "gHi"})
+    eq('\nE322: line number out of range: 1 past the end\nE320: Cannot find line 2',
+       redir_exec('2,$luado vim.api.nvim_command("%d") return linenr'))
+    eq({''}, curbufmeths.get_lines(0, -1, false))
+  end)
+  it('fails on errors', function()
+    eq([[Vim(luado):E5109: Error while creating lua chunk: [string "<VimL compiled string>"]:1: unexpected symbol near ')']],
+       exc_exec('luado ()'))
+    eq([[Vim(luado):E5111: Error while calling lua function: [string "<VimL compiled string>"]:1: attempt to perform arithmetic on global 'liness' (a nil value)]],
+       exc_exec('luado return liness + 1'))
+  end)
+  it('fails in sandbox when needed', function()
+    curbufmeths.set_lines(0, 1, false, {"ABC", "def", "gHi"})
+    eq('\nE48: Not allowed in sandbox: sandbox luado runs = (runs or 0) + 1',
+       redir_exec('sandbox luado runs = (runs or 0) + 1'))
+    eq(NIL, funcs.luaeval('runs'))
+  end)
+  it('works with long strings', function()
+    local s = ('x'):rep(100500)
+    eq('', redir_exec(('luado return "%s"'):format(s)))
+    eq({s}, curbufmeths.get_lines(0, -1, false))
+  end)
+end)