first transform, then visit, to not get incorrect line markers

low-priority QoL - unless flake8-trio is used in automated environments.

Failing test:

def test_line_numbers_match_end_result():
    text = """import trio
with trio.move_on_after(10):
  ...

trio.sleep(0)
"""
    plugin = Plugin.from_source(text)
    initialize_options(plugin, args=["--enable=TRIO100,TRIO115", "--autofix=TRIO100"])
    errors = tuple(plugin.run())
    new_source = plugin.module.code
    assert errors[1].line == plugin.module.code.split('\n').index('trio.sleep(0)')+1

the assertion fails with 5 != 4 as the line numbers of objects are never updated once parsed when initiating the plugin.

The best way to fix this would probably, as the header suggest, be to first make a pass where all enabled autofixers are run - with autofixed errors being printed out with old and/or no line markers. Then the file is reparsed, and enabled visitors are run on the file.

Start with the failing test test_line_numbers_match_end_result and trace Plugin.from_source, initialize_options, and plugin.run. Check how autofixers and visitors are sequenced and how line markers are retained. Done means autofixes run before reparsing, visitors see the transformed source, and the assertion reports the correct line for trio.sleep(0).