BOLT 12 {Static}Invoices: expose more is_expired methods

In upcoming commits, we need to check whether a static invoice or its underlying
offer is expired in no-std builds. Here we expose the methods to do so. The
methods could instead be kept private to the crate, but they seem potentially
useful.

Author: valentinewallace

lightning/src/offers/invoice.rs

@@ -1223,6 +1223,10 @@ impl InvoiceContents {
 		is_expired(self.created_at(), self.relative_expiry())
 	}
 
+	fn is_expired_no_std(&self, duration_since_epoch: Duration) -> bool {
+		self.created_at().saturating_add(self.relative_expiry()) < duration_since_epoch
+	}
+
 	fn payment_hash(&self) -> PaymentHash {
 		self.fields().payment_hash
 	}

lightning/src/offers/invoice_macros.rs

@@ -131,6 +131,11 @@ macro_rules! invoice_accessors_common { ($self: ident, $contents: expr, $invoice
 		$contents.is_expired()
 	}
 
+	/// Whether the invoice has expired given the current time as duration since the Unix epoch.
+	pub fn is_expired_no_std(&$self, duration_since_epoch: Duration) -> bool {
+		$contents.is_expired_no_std(duration_since_epoch)
+	}
+
 	/// Fallback addresses for paying the invoice on-chain, in order of most-preferred to
 	/// least-preferred.
 	pub fn fallbacks(&$self) -> Vec<Address> {

lightning/src/offers/static_invoice.rs

@@ -395,6 +395,18 @@ impl StaticInvoice {
 		self.signature
 	}
 
+	/// Whether the [`Offer`] that this invoice is based on is expired.
+	#[cfg(feature = "std")]
+	pub fn is_offer_expired(&self) -> bool {
+		self.contents.is_expired()
+	}
+
+	/// Whether the [`Offer`] that this invoice is based on is expired, given the current time as
+	/// duration since the Unix epoch.
+	pub fn is_offer_expired_no_std(&self, duration_since_epoch: Duration) -> bool {
+		self.contents.is_offer_expired_no_std(duration_since_epoch)
+	}
+
 	#[allow(unused)] // TODO: remove this once we remove the `async_payments` cfg flag
 	pub(crate) fn is_from_same_offer(&self, invreq: &InvoiceRequest) -> bool {
 		let invoice_offer_tlv_stream =
@@ -411,7 +423,6 @@ impl InvoiceContents {
 		self.offer.is_expired()
 	}
 
-	#[cfg(not(feature = "std"))]
 	fn is_offer_expired_no_std(&self, duration_since_epoch: Duration) -> bool {
 		self.offer.is_expired_no_std(duration_since_epoch)
 	}
@@ -528,6 +539,10 @@ impl InvoiceContents {
 		is_expired(self.created_at(), self.relative_expiry())
 	}
 
+	fn is_expired_no_std(&self, duration_since_epoch: Duration) -> bool {
+		self.created_at().saturating_add(self.relative_expiry()) < duration_since_epoch
+	}
+
 	fn fallbacks(&self) -> Vec<Address> {
 		let chain = self.chain();
 		self.fallbacks