[BenCodez]

Summary

Fix several deterministic AdvancedCore correctness issues outside the reward subsystem.

Thread safety

• remove System.exit(0) from FileThread.ReadThread interruption handling
• remove System.exit(0) from the deprecated Thread.ReadThread helper
• treat interruption as normal shutdown: restore the interrupt flag and exit the loop
• use each worker thread's own interruption state instead of the outer thread reference

Inventory scheduling

• fix BInventory.addUpdatingButton(...) to use its interval argument as the fixed-delay period instead of incorrectly reusing the initial delay
• retain existing timer cancellation behavior

MiscUtils correctness

• make addSeconds(Date, int) add to the supplied date instead of the current time
• increment stagger delay for each list command so staggered commands actually run on successive ticks
• normalize leading / consistently before Bukkit console command dispatch, including list/staggered and single-command paths

Tests

• add MiscUtilsTest for supplied-date arithmetic, stagger delay progression, and slash stripping
• add BInventoryTest for initial delay/update interval and future cancellation
• add ThreadInterruptionTest verifying both legacy worker threads terminate normally when interrupted

This PR is intentionally focused on deterministic correctness fixes and does not change reward behavior or configuration.