Add some missing Optional type annotations to interval_range and read_sql

[MarcoGorelli]

These are some cases where the overloads indicate that they are meant to match the parameter defaults, which in all these cases are = None. However, None is currently missing from the annotations for these parameters

• Closes #xxxx (Replace xxxx with the Github issue number)
• Tests added: Please use assert_type() to assert the type of any return value

[Dr-Irv]

If you want to fix the other defaults for read_sql() that would be good as well, but not a problem if you don't.

[MarcoGorelli]

Thanks @Dr-Irv for your review!

I noticed these missing | Nones while looking into a follow-up to #1293. There's quite a few more that are missing. For ease of review, OK if we start with fixing the missing | Nones, and in a follow-up I'll address the defaults?

[Dr-Irv]

I noticed these missing | Nones while looking into a follow-up to #1293. There's quite a few more that are missing. For ease of review, OK if we start with fixing the missing | Nones, and in a follow-up I'll address the defaults?

Yes, that's fine.

[Dr-Irv]

Thanks @MarcoGorelli