Refactor session views into separate files

[karbassi]

Refactors the session-related views into separate files for improved organization and readability, and adds comprehensive tests for each view.

• Splits the original sessions.py logic into four separate files: detail.py, signup.py, password.py, and calendar.py, each handling a specific aspect of session management.
• Implements comprehensive documentation within each new view file to explain the purpose and functionality of the code.
• Adds test files for each of the new view files, ensuring proper test coverage and functionality verification for session detail, sign-up, password protection, and calendar views.
• Modifies the original sessions.py to redirect imports to the new structure, streamlining the codebase and enhancing maintainability.

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