Use GNU parallel to speed up

[yegle]

Example command:

parallel --halt now,success=1 -u -N0 python vanity_npub.py -j1 TARGET ::: {0..$(nproc)}

Explanation:

• --halt now,success=1: stop all commands as soon as one of them returned success
• -u: do not group output by commands
• -N0: the command takes 0 argument (essentially, run the same command X times)
• ::: {0..$(nproc)}: generate # of commands matches # of CPUs