Fix code review findings: retry semantics, rollback token, batch progress, and clean up

[JusterZhu]

Summary

Address findings from the 9-PR Drivelution refactoring code review.

Fixes

• P0: RetryPolicy exception semantics (last retry exception leakage)
• P0: Rollback uses expired cancellation token
• P0: BatchUpdateAsync Interlocked progress calculation
• P0: VerifyInstallationAsync triggers unnecessary rollback on pnputil failure
• P1: CommandRunner missing process kill on cancellation
• P1: DrivelutionFactory inconsistency (CreateValidator/CreateBackup still throw on macOS)
• P1: Factory error message missing macOS
• P2: Remove dead ReportProgress method
• P2: Merge RetryPolicy duplicate delay calculation
• P2: Simplify QuickUpdateAsync overloads

Closes #298