feat: Add private-leaderboard command

[byarr]

Adds a private leaderboard command to print the results of a given private leaderboard.

Example output is similar to that on the website - but without colors or headers.

1       142     ★★★★★★★★★★★                     byarr
2       129     ★★★★★★★★★★★                     Someone else
3       125     ★★★★★★★★★★★                     anonymous user #122345
4       108     ★★★★★★★★★★★                     Bob Jones
5       87      ★★★★★★★★★★★                     Jane Doe
6       83      ★★★★★★★★★★★                     abcdef
7       78      ★★★.★★★★★★★                     anonymous user #12344
8       28      ★★★★★★.....                     Some one

[scarvalhojr]

That looks great, thank you!

[scarvalhojr]

We don't need args here

[scarvalhojr]

We could simplify this by implementing TryFrom<&Value> for Member so we only load the fields we need. We could even count the number of stars for each day then rather than when we're writing to the terminal. This would avoid all the fields xxx are never read clippy warnings.

[scarvalhojr]

I think instead of calling puzzle_year_day we need a new function. Something that: 1) unwraps the year if given or returns the latest event year, e.g. let year = args.year.unwrap_or_else(latest_event_year); and 2) returns the last unlocked day for the selected year.

[scarvalhojr]

I'll merge this as it is and will do some minor changes to make Clippy happy