Expand VIF UNPACK V2 and V3 lanes

[GTTeancum]

Summary

• expand V2 UNPACK inputs as XYXY instead of leaving Z/W stale
• source V3 W from the next packed component when XYZ remains within the source quadword
• zero V3 W when XYZ ends exactly on a 16-byte source boundary
• add focused V2-8 and V3-16 regression coverage, including protection against consuming the following VIF command as W

PCSX2 documents these hardware-tested behaviors in its VIF unpack implementations. Games rely on the otherwise-documented-as-indeterminate V2/V3 lanes.

This branch is based directly on main; it is independent of #232.

Verification

• MINITEST_FILTER="VIF UNPACK V2 duplicates": 1 passed, 0 failed
• MINITEST_FILTER="VIF UNPACK V3 zeros W at a quadword boundary": 1 passed, 0 failed
• Release build with MSBuild, one worker

The unfiltered suite has pre-existing failures outside PS2Memory and includes long scheduler tests; the focused regression cases pass cleanly.