Fix SUROM PRG bank selection

[SaveEditors]

Summary

• retain the selected MMC1 PRG bank and reapply it after control or CHR0 page changes
• map both SUROM PRG windows within the selected 256 KB page
• preserve existing power-on, 4 KB CHR-mode, non-SUROM, and legacy save-state behavior
• add synthetic coverage for all PRG modes, both outer pages, write ordering, and state restoration

Root cause

Mapper 1 calculated upper-page banks in inconsistent units and only updated PRG mapping after register 3 writes. The fixed PRG window also remained on the global last bank instead of following the selected SUROM page.

Fixes #732

Testing

• npm run build
• npm test
• cd web && npm run build
• cd web && npm test