Improve memory consumption: del page.markdown

[FrancoisCapon]

Hi,

This pull request follow the discussion on the #2669 issue and improve only the "First phase" because in this case theory and graph match: more 1 MB earned

The graph show the full memory consumption of mkdocs because I put the tracemalloc.start() at the beginning of the "main".

traefik-official-docs/content$ du -ch *.md ./*/*.md ./*/*/*.md | tail
28K	./routing/providers/kubernetes-gateway.md
24K	./routing/providers/kubernetes-ingress.md
20K	./routing/providers/kv.md
16K	./routing/providers/marathon.md
20K	./routing/providers/rancher.md
4,0K	./routing/providers/service-by-label.md
40K	./routing/routers/index.md
40K	./routing/services/index.md
8,0K	./user-guides/crd-acme/index.md
1,2M	total

[FrancoisCapon]

Yes, one test failed because the attribute page.markdown no more exist when the assertion check the markdown content.

======================================================================
ERROR: test_populate_page_dirty_modified (tests.build_tests.BuildTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/runner/work/mkdocs/mkdocs/mkdocs/tests/base.py", line 79, in wrapper
    return fn(self, td, *args)
  File "/home/runner/work/mkdocs/mkdocs/mkdocs/tests/build_tests.py", line 300, in test_populate_page_dirty_modified
    self.assertTrue(page.markdown.startswith('# Welcome to MkDocs'))
AttributeError: 'Page' object has no attribute 'markdown'

----------------------------------------------------------------------

    @tempdir(files={'testing.html': '<p>page content</p>'})
    def test_populate_page_dirty_modified(self, site_dir):
        cfg = load_config(site_dir=site_dir)
        file = File('testing.md', cfg['docs_dir'], cfg['site_dir'], cfg['use_directory_urls'])
        page = Page('Foo', file, cfg)
        build._populate_page(page, cfg, Files([file]), dirty=True)
        # self.assertTrue(page.markdown.startswith('# Welcome to MkDocs'))
        self.assertTrue(page.content.startswith('<h1 id="welcome-to-mkdocs">Welcome to MkDocs</h1>'))

I let the testers update the test so the modification can pass the tests. ✔️

[pawamoy]

Hi @FrancoisCapon, sorry you didn't get any news on this, and thanks for your patience. In the mentioned issue @oprypin said he wanted to verify the results himself, so I'll let him update us on that (if you're still interested by this memory optimization of course @oprypin. I think we should all be interested in optimizations anyway 😋 ).