Split SessionsPage into subpages

[jf-x-dev]

This is a very large PR which splits the massive SessionsPage into the subpages:

• SessionsChildrenPage
• SessionsConsentPage
• SessionsEditPage
• SessionsOverviewPage
• SessionsPatientPage
• SessionsPatientSessionActivityPage
• SessionsPsdPage
• SessionsRecordVaccinationsPage
• SessionsRegisterPage
• SessionsSearchPage
• SessionsTriagePage
• SessionsVaccinationWizardPage

This makes the file sessions.py easier to read, understand and work on. It also makes our code adhere more strictly to the Playwright POM. Some other things happened unintentionally during this refactor which would be pretty annoying to split into other commits / PRs:

• Some unused functions/locators were removed
• The "cleanup" step, where all session dates are deleted at the end of a test run, was removed. This is because you can no longer delete all session dates at a session. The tests still work as they currently only schedule session dates if necessary.

There are some less positive effects that this PR has:

• sessions.py is still very large
• Tests get longer as many utility functions were split up
• Some of our tests now have a very large number of parameters, due to each page having its own fixture.

These will be addressed in future PRs.

Due to AI usage etc, the split was done all at once which makes it very hard to review. At the very least, it would be worth checking that the new page objects have appropriate names.