fix: disable lifecycle scripts during npm diff

[arthurianresolve]

Fixes #9955

Summary

• Force ignoreScripts: true when npm diff calls libnpmdiff.
• Prevent local directory operands from running prepare while an inspection-only diff is being created.
• Add command-level coverage that verifies the option cannot be overridden by normal flat options.

Testing

• node_modules\.bin\tap.cmd --no-check-coverage test/lib/commands/diff.js — passed.
• End-to-end temporary-package reproduction — npm diff exited successfully and did not create the prepare marker.

Compatibility note

Generated files that exist only after running prepare will no longer be materialized by npm diff. This is the intended behavior change for an inspection command; registry-to-registry and ordinary diff behavior remain unchanged.