Make the test suite pass on Windows

The Filesystem module stored the paths of an iOS dump with the separator
of the system checking it, so on Windows the process and file path
indicators, which split paths on "/", never matched. It now stores them
as POSIX paths.

The rest are test fixes:
- the completion install tests also redirect USERPROFILE, which
  Path.home() reads on Windows; they wrote to the real home folder;
- the plugin table helpers accept the light header Rich draws on
  consoles that cannot show the heavy one;
- the completion test quotes the command path, whose backslashes were
  dropped when COMP_WORDS was split;
- tests that need symbolic links or the sqlite3 binary are skipped when
  those are not available;
- two assertions no longer depend on the path separator or on the line
  ending text mode writes.

tests/test_completion.py

@@ -43,6 +43,7 @@ class TestCompletionCommand:
 
     def test_completion_install_updates_bashrc_once(self, tmp_path, monkeypatch):
         monkeypatch.setenv("HOME", str(tmp_path))
+        monkeypatch.setenv("USERPROFILE", str(tmp_path))
         runner = CliRunner()
 
         result = runner.invoke(mvt_cli, ["completion", "bash", "--install"])
@@ -67,6 +68,7 @@ class TestCompletionCommand:
         self, tmp_path, monkeypatch
     ):
         monkeypatch.setenv("HOME", str(tmp_path))
+        monkeypatch.setenv("USERPROFILE", str(tmp_path))
         runner = CliRunner()
 
         result = runner.invoke(mvt_cli, ["completion", "fish", "--install"])