Improve Session Handling in restore_boot() to Prevent Unnecessary session_start() Calls

[saranshj4]

Is your feature request related to a problem? Please describe.

The restore_boot() function currently triggers session_start() on every load across frontend, backend, and AJAX calls, resulting in thousands of log entries with messages like "session_start() will be ignored because a session is already active" when other plugins or custom code also initiate sessions. This causes session conflicts, as the BackWPUp session isn't recognized by other session_start() checks.

Describe the solution you'd like
Comment from @danielhuesken: https://group-onecom.slack.com/archives/C05CYKYC78W/p1728977420819399?thread_ts=1728976672.165849&cid=C05CYKYC78W

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
User ticket: https://wordpress.org/support/topic/session-errors-2/#post-18080021

[saranshj4]

https://wordpress.org/support/topic/php-warning-failed-to-read-session-data/

[saranshj4]

https://wordpress.org/support/topic/session-errors-2/#post-18095578