[bindings] No-export RouteHopCandidate lifetime'd fields

The bindings cannot express lifetimes, so exposing any field which
is a reference (and not `clone`-able, at least for garbage
collected language bindings) is unsafe for those expecting a
high-level interface.

Thus, we simply no-export the `RouteHopCandidate` inner struct
fields which are references (there are relevant accessors for them
anyway).

Author: TheBlueMatt

lightning/src/routing/router.rs

@@ -1146,8 +1146,12 @@ pub struct FirstHopCandidate<'a> {
 	/// has been funded and is able to pay), and accessor methods may panic otherwise.
 	///
 	/// [`find_route`] validates this prior to constructing a [`CandidateRouteHop`].
+	///
+	/// This is not exported to bindings users as lifetimes are not expressable in most languages.
 	pub details: &'a ChannelDetails,
 	/// The node id of the payer, which is also the source side of this candidate route hop.
+	///
+	/// This is not exported to bindings users as lifetimes are not expressable in most languages.
 	pub payer_node_id: &'a NodeId,
 }
 
@@ -1156,6 +1160,8 @@ pub struct FirstHopCandidate<'a> {
 pub struct PublicHopCandidate<'a> {
 	/// Information about the channel, including potentially its capacity and
 	/// direction-specific information.
+	///
+	/// This is not exported to bindings users as lifetimes are not expressable in most languages.
 	pub info: DirectedChannelInfo<'a>,
 	/// The short channel ID of the channel, i.e. the identifier by which we refer to this
 	/// channel.
@@ -1166,8 +1172,12 @@ pub struct PublicHopCandidate<'a> {
 #[derive(Clone, Debug)]
 pub struct PrivateHopCandidate<'a> {
 	/// Information about the private hop communicated via BOLT 11.
+	///
+	/// This is not exported to bindings users as lifetimes are not expressable in most languages.
 	pub hint: &'a RouteHintHop,
 	/// Node id of the next hop in BOLT 11 route hint.
+	///
+	/// This is not exported to bindings users as lifetimes are not expressable in most languages.
 	pub target_node_id: &'a NodeId
 }
 
@@ -1176,6 +1186,8 @@ pub struct PrivateHopCandidate<'a> {
 pub struct BlindedPathCandidate<'a> {
 	/// Information about the blinded path including the fee, HTLC amount limits, and
 	/// cryptographic material required to build an HTLC through the given path.
+	///
+	/// This is not exported to bindings users as lifetimes are not expressable in most languages.
 	pub hint: &'a (BlindedPayInfo, BlindedPath),
 	/// Index of the hint in the original list of blinded hints.
 	///
@@ -1191,6 +1203,8 @@ pub struct OneHopBlindedPathCandidate<'a> {
 	/// cryptographic material required to build an HTLC terminating with the given path.
 	///
 	/// Note that the [`BlindedPayInfo`] is ignored here.
+	///
+	/// This is not exported to bindings users as lifetimes are not expressable in most languages.
 	pub hint: &'a (BlindedPayInfo, BlindedPath),
 	/// Index of the hint in the original list of blinded hints.
 	///