feat(datetime): publicly import std.datetime.stopwatch in std.datetime

[schveiguy]

Note, the removal of the offending std.datetime.benchmark function occurred June 2021, and TickDuration itself is about to be removed. There is no reason not to import this module implicitly like all other models.

Rationale

The reason for the lack of public import is long gone. Let's see if anything breaks.

Pre-review checklist

• I have performed a self-review of my code.
• If my PR fixes a bug or introduces a new feature, I have added thorough tests.
• If my changes are non-trivial and do not concern a reported issue, I have added a changelog entry.

LLM/AI disclosure

I wrote this myself! I deserve three gold stars.

[schveiguy]

This should have a changelog, don't merge yet.

[Herringway]

⭐⭐⭐

[0xEAB]

I wrote this myself! I deserve three gold stars.

Here you are: 🏅🏅🏅

[schveiguy]

OK, changelog added.

[thewilsonator]

Style CI fails

Check for trailing whitespace
grep -nr '[[:blank:]]$' $(find etc std -name '*.d'); test $? -eq 1
std/utf.d:3740: *      Otherwise, `r` is converted to its corresponding string type.

[0xEAB]

Rebasing should fix that. (#11096)

[0xEAB]

Rebased.