Add from_nanoseconds to FFI PlainDateTime (#583)

Closes #579.

Author: nekevss

temporal_capi/bindings/c/PlainDateTime.h

@@ -6,6 +6,7 @@ pub mod ffi {
     use crate::calendar::ffi::{AnyCalendarKind, Calendar};
     use crate::duration::ffi::Duration;
     use crate::error::ffi::TemporalError;
+    use crate::instant::ffi::I128Nanoseconds;
     use crate::options::ffi::{
         ArithmeticOverflow, DifferenceSettings, DisplayCalendar, RoundingOptions,
         ToStringRoundingOptions,
@@ -135,6 +136,22 @@ pub mod ffi {
             let zdt = crate::zoned_date_time::zdt_from_epoch_ms_with_provider(ms, tz.into(), p)?;
             Ok(Box::new(Self(zdt.to_plain_date_time())))
         }
+        #[cfg(feature = "compiled_data")]
+        pub fn from_epoch_nanoseconds<'p>(
+            ns: I128Nanoseconds,
+            tz: TimeZone,
+            p: &Provider<'p>,
+        ) -> Result<Box<Self>, TemporalError> {
+            Self::from_epoch_nanoseconds_with_provider(ns, tz, &Provider::compiled())
+        }
+        pub fn from_epoch_nanoseconds_with_provider<'p>(
+            ns: I128Nanoseconds,
+            tz: TimeZone,
+            p: &Provider<'p>,
+        ) -> Result<Box<Self>, TemporalError> {
+            let zdt = crate::zoned_date_time::zdt_from_epoch_ns_with_provider(ns, tz.into(), p)?;
+            Ok(Box::new(Self(zdt.to_plain_date_time())))
+        }
         pub fn with(
             &self,
             partial: PartialDateTime,

temporal_capi/bindings/cpp/temporal_rs/PlainDateTime.d.hpp

@@ -1,4 +1,5 @@
 use crate::error::ffi::TemporalError;
+use crate::instant::ffi::I128Nanoseconds;
 use crate::provider::ffi::Provider;
 use temporal_rs::options::RelativeTo;
 
@@ -721,6 +722,17 @@ pub(crate) fn zdt_from_epoch_ms_with_provider<'p>(
     .map_err(Into::into)
 }
 
+pub(crate) fn zdt_from_epoch_ns_with_provider<'p>(
+    ns: I128Nanoseconds,
+    time_zone: temporal_rs::TimeZone,
+    p: &Provider<'p>,
+) -> Result<temporal_rs::ZonedDateTime, TemporalError> {
+    let instant = temporal_rs::Instant::try_new(ns.into())?;
+    with_provider!(p, |p| instant
+        .to_zoned_date_time_iso_with_provider(time_zone, p))
+    .map_err(Into::into)
+}
+
 impl TryFrom<ffi::PartialZonedDateTime<'_>> for temporal_rs::partial::PartialZonedDateTime {
     type Error = TemporalError;
     fn try_from(other: ffi::PartialZonedDateTime<'_>) -> Result<Self, TemporalError> {