manually implement Copy on DateTime<Tz>

[little-dude]

derive generates the following impls:

impl<Tz: ::core::marker::Copy + TimeZone> ::core::marker::Copy for DateTime<Tz>
where
    Tz::Offset: ::core::marker::Copy,
{}

impl<Tz: ::core::clone::Clone + TimeZone> ::core::clone::Clone for DateTime<Tz>
where
    Tz::Offset: ::core::clone::Clone,
{
    #[inline]
    fn clone(&self) -> DateTime<Tz> {
        DateTime {
            datetime: ::core::clone::Clone::clone(&self.datetime),
            offset: ::core::clone::Clone::clone(&self.offset),
        }
    }
}

In the Copy impl, the Tz: Copy bound is un-necessary. Note that in the Clone impl, he Tz: Clone is also un-necessary, but it's implied by the TimeZone bound anyway, so there's not point having a manual implementation of Clone.

Fixes #1571

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.82%. Comparing base (760eb66) to head (359d1e2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1572   +/-   ##
=======================================
  Coverage   91.82%   91.82%           
=======================================
  Files          37       37           
  Lines       18173    18173           
=======================================
  Hits        16687    16687           
  Misses       1486     1486           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[little-dude]

Closing in favor of #1573

[pitdicker]

We were pretty much at the same time, thank you for working on it!