Add DateVector and DatetimeVector default ctors (closes #1384)

[eddelbuettel]

As discussed in #1384 these were omitted in earlier implementations, mostly due to sloppy thinking and a bias towards the data(time) in std::vector use seen in another library that was interfaced at the very (very !!) beginning of Rcpp. But that is simply not the R way of things, and while we did on pass over this (when the then newDate*Vector classes were added we still did not add empty constructors. Which I now use more often for base types (think integer() etc) so we should have something like that here too.

The PR itself is pretty minimal and just adds these new ctors, does not alter existing interfaces, and adds a handful of test predicates.

A complete reverse-dependency check is running but it will (as usual) be a good moment before it is done.

Checklist

• Code compiles correctly
• R CMD check still passes all tests
• Preferably, new tests were added which fail without the change
• Document the changes by file in ChangeLog

[Copilot]

Pull Request Overview

This PR adds default constructors for DateVector and DatetimeVector to align the Rcpp API with typical R conventions.

• Added default constructors in newDateVector.h and newDatetimeVector.h
• Added corresponding tests in inst/tinytest/test_date.R and inst/tinytest/cpp/dates.cpp
• Updated copyright years to reflect the current year

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
inst/tinytest/test_date.R	Added tests to validate that the default constructors create empty vectors with correct class types
inst/tinytest/cpp/dates.cpp	Added exportable functions for default DateVector and DatetimeVector creation
inst/include/Rcpp/date_datetime/newDatetimeVector.h	Added a default constructor that sets the class using the provided timezone
inst/include/Rcpp/date_datetime/newDateVector.h	Added a default constructor that sets the class
ChangeLog	Documented the new default constructors and corresponding tests

[Enchufa2]

Small and focused, as you said. No further comments.

[eddelbuettel]

Thanks! I will summarise the reverse depends run in a bit. It may be that we tickle a change here or there in which case we could table this for the release after the next (which is coming up in five weeks) (or could try to cram it in, to be seen).

[kevinushey]

LGTM!

[eddelbuettel]

Reverse-depends worked out as well:

• run one had a few new depends, plus depends on arrow and RcppPlanc neither one will install on that old machine which cannot do AVX2 but the configuration scripts are not careful enough
• run two is cleaner and just two known (caused by their upstream) issues

With that we're good so ...