chore: add box to scalar expr in interactive mode

[ncclementi]

This is an attempt to close #9247 and possible the discussion around #8833

I'm using rich Panel and the box.SQUARE style to wrap scalar values into a box. There are multiple styles (see https://rich.readthedocs.io/en/stable/appendix/box.html), I chose the one that looks the most similar to what we have now.

TODO:

• Do we need a tests for this? I wasn't quite sure how to add a test for it.
• Modify doctests accordingly if we like this change

Closes #9247

Here is how it renders in ipython.

In [1]: import ibis

In [2]: ibis.options.interactive = True

In [3]: ibis.literal(1).nullif(1)
Out[3]: 
┌──────┐
│ None │
└──────┘

In [4]: ibis.literal(1).nullif(0)
Out[4]: 
┌───┐
│ 1 │
└───┘

In [5]: ibis.literal("abcdefghi").substr(3)
Out[5]: 
┌──────────┐
│ 'defghi' │
└──────────┘

In [6]: print(ibis.literal("abcdefghi").substr(3))
┌──────────┐
│ 'defghi' │
└──────────┘

In [7]: print(ibis.literal(True))
┌──────┐
│ True │
└──────┘

In [8]: import datetime

In [9]: date = datetime.datetime(2015, 1, 1, 12, 34, 56)

In [10]: print(ibis.literal(date))
┌──────────────────────────────────┐
│ Timestamp('2015-01-01 12:34:56') │
└──────────────────────────────────┘

[ncclementi]

After chatting in triage we are ok with the change, I will go ahead and modify the doctests to match the new repr.