Defer EE time-slice preemption while interrupts are disabled

[GTTeancum]

Summary

• gate synthetic EE scheduler preemption on Status.IE/EIE and EXL/ERL
• keep deferred reschedules pending so the first checkpoint after EI can service them
• add a regression test covering a same-priority time-slice expiry across DI/EI

Why

PS2 software uses DI/EI around critical list and allocator mutations. The runtime's interrupt dispatch observes those bits, but synthetic time-slice preemption did not. That allowed a ready peer to run during an intentionally transient list state and consume partially updated pointers.

Testing

• clean Release build from upstream main
• ps2x_tests: 426 passed, 0 failed
• runtime validation through 1,500 rendered frames: the previously reproducible invalid list lookup and downstream indirect-branch corruption no longer occur