Update to latest tzdb (what will become tzdb 0.5.0) (#387)

* Apply `not_a_century` change HowardHinnant/date@0ef86f1

* Apply `read_signed()` related patches

The upstream `date::read_signed()` has changed and now includes a `+` or `-` in the actual count of parsed values. This actually means that `%Y` can no longer parse `-1000` as a year without it explicitly being `%5Y`, which is something we need to add tests for if this change is here to stay.

Without this change, many tests break because `%z` no longer parses correctly. We preemptively look for `-` and `+`, but previously the fallthrough `read()` call would consume them without reducing the `M` max count and now it no longer does, so we have to `is.get()` to advance manually.

HowardHinnant/date@ab37c36

HowardHinnant/date@5d22595

* Apply dead code removal change HowardHinnant/date@cd3c579

* Add remote on tzdb

* Let cpp11.R regenerate itself

* Apply `rs{}` to `ru{}` related changes HowardHinnant/date@32ecb2a

* NEWS bullet

* Fix indentation issue clangd identified

* Add test for negative year behavior

* NEWS bullet

Author: DavisVaughan

DESCRIPTION

@@ -20,7 +20,7 @@ Imports:
     cli (>= 3.6.1),
     lifecycle (>= 1.0.3),
     rlang (>= 1.1.0),
-    tzdb (>= 0.4.0),
+    tzdb (>= 0.4.0.9000),
     vctrs (>= 0.6.1)
 Suggests:
     covr,
@@ -33,7 +33,7 @@ Suggests:
     withr
 LinkingTo:
     cpp11 (>= 0.5.1),
-    tzdb (>= 0.4.0)
+    tzdb (>= 0.4.0.9000)
 VignetteBuilder:
     knitr
 Config/build/compilation-database: true
@@ -45,3 +45,5 @@ Encoding: UTF-8
 LazyData: true
 Roxygen: list(markdown = TRUE)
 RoxygenNote: 7.3.2
+Remotes:
+    r-lib/tzdb

NEWS.md

@@ -1,5 +1,15 @@
 # clock (development version)
 
+* `%Y`, `%F`, `%G`, and `%c` now parse up to 4 _characters_ by default, rather
+  than 4 _digits_. This is more in line with the C++20 specification and was a
+  change made in the upstream `<date.h>` parser. Practically, this means that
+  negative years such as `-1000-01-01` will no longer parse with `%Y-%m-%d`, and
+  instead requires `%5Y-%m-%d` to capture the leading `-` (#387).
+
+* tzdb >=0.5.0 is required. Note that older versions of clock are not compatible
+  with tzdb 0.5.0 and above, so if you are having issues (particularly with
+  parsing) please make sure that both clock and tzdb are fully updated (#387).
+
 * Fixed `-Wdeprecated-literal-operator` reported by clang (#386,
   @MichaelChirico).