fix(interrupts): honor delegation when selecting in-order interrupts

[murdoa]

Supervisor software, timer and external interrupts currently participate in selection only through sip/sie. When their mideleg bit is clear, those views hide the source, so an enabled pending interrupt is dropped instead of targeting M-mode. For example, setting STIP, STIE and MIE with mideleg.STI=0 never reaches mtvec.

Select the six standard sources from the canonical mip & mie state and use delegation plus the current privilege to determine eligibility. This also gives M-target interrupts priority over S-target interrupts: an undelegated SSI must outrank a delegated SEI, despite its lower source priority.

The candidate remains registered, but is offered to the executor only while it matches the currently eligible winner. Writes to interrupt masks/delegation, privilege changes, or a newly pending higher-priority source therefore cannot leave a stale candidate available for acceptance. Once the executor accepts a trap, its existing completion and retirement path is unchanged.

Scope

Non-H in-order cores, with both static and microcoded execution. The H/OoO selector is unchanged. WFI remains a legal NOP, and there are no status-stack or reservation-policy changes.

Tests

Added RV32/RV64 cases for M/S/U delivery, global and local masks, target/source priority, candidate revalidation during CSR instructions, and completion after an accepted interrupt's source deasserts. Separate controls exercise WFI progress and M/S trap/return status preservation.

All 269 cases pass, including 129 existing controls for interrupt register integrity, AMO indivisibility, CSR aliases, MPRV, FCSR and VS trap delegation. Baseline fails 32 architectural delivery/priority assertions and 16 candidate-interface checks; all 221 baseline passes are preserved.