[Feature]: Support display private key discreetly for keys export

[Halimao]

Summary

Ref #18662

simd keys export <name> --unsafe -unarmored-hex will also show unarmored private key in output, we can show it discreetly on an alternate screen.

Problem Definition

It would be more safe if we display unarmored private key on an alternate screen

Proposed Feature

After we run `simd keys export --unsafe -unarmored-hex, the unarmored private key will show on an alternate screen, with some prompt msg. With 'Enter' key press, will bring user back to original screen.

if user provide --indiscreet flag, will show on current terminal directly.

[Halimao]

I will draft a pr for this issue later.