MPT-19124 speed up tests

[jentyk]

Closes MPT-19124

• Converted many pytest fixtures across the e2e test suite from function scope to session scope (fixtures now created once per test session and reused)
• Scope changes applied across numerous conftest.py files under tests/e2e (including the top-level e2e conftest and multiple helpdesk, accounts, billing, catalog, commerce, notifications, audit, billing, and other module subdirectories)
• Fixed pdf_fd fixture to use a context-managed yielding implementation (properly opening/closing the file handle while yielding the same file object)
• Result: faster e2e test runs due to reduced fixture setup/teardown overhead