Tag types used for the TLV macros with (C-not exported)

Obviously bindings users can't use the Rust TLV-implementation
macros, so there's no reason to export typsed used exclusively by
them.

Author: TheBlueMatt

lightning/src/util/ser.rs

@@ -89,6 +89,8 @@ impl Writer for VecWriter {
 
 /// Writer that only tracks the amount of data written - useful if you need to calculate the length
 /// of some data when serialized but don't yet need the full data.
+///
+/// (C-not exported) as manual TLV building is not currently supported in bindings
 pub struct LengthCalculatingWriter(pub usize);
 impl Writer for LengthCalculatingWriter {
 	#[inline]
@@ -100,6 +102,8 @@ impl Writer for LengthCalculatingWriter {
 
 /// Essentially [`std::io::Take`] but a bit simpler and with a method to walk the underlying stream
 /// forward to ensure we always consume exactly the fixed length specified.
+///
+/// (C-not exported) as manual TLV building is not currently supported in bindings
 pub struct FixedLengthReader<R: Read> {
 	read: R,
 	bytes_read: u64,
@@ -155,6 +159,8 @@ impl<R: Read> LengthRead for FixedLengthReader<R> {
 
 /// A [`Read`] implementation which tracks whether any bytes have been read at all. This allows us to distinguish
 /// between "EOF reached before we started" and "EOF reached mid-read".
+///
+/// (C-not exported) as manual TLV building is not currently supported in bindings
 pub struct ReadTrackingReader<R: Read> {
 	read: R,
 	/// Returns whether we have read from this reader or not yet.
@@ -289,6 +295,8 @@ impl<T: Readable> MaybeReadable for T {
 }
 
 /// Wrapper to read a required (non-optional) TLV record.
+///
+/// (C-not exported) as manual TLV building is not currently supported in bindings
 pub struct RequiredWrapper<T>(pub Option<T>);
 impl<T: Readable> Readable for RequiredWrapper<T> {
 	#[inline]
@@ -311,6 +319,8 @@ impl<T> From<T> for RequiredWrapper<T> {
 
 /// Wrapper to read a required (non-optional) TLV record that may have been upgraded without
 /// backwards compat.
+///
+/// (C-not exported) as manual TLV building is not currently supported in bindings
 pub struct UpgradableRequired<T: MaybeReadable>(pub Option<T>);
 impl<T: MaybeReadable> MaybeReadable for UpgradableRequired<T> {
 	#[inline]
@@ -591,6 +601,8 @@ impl Readable for [u16; 8] {
 
 /// A type for variable-length values within TLV record where the length is encoded as part of the record.
 /// Used to prevent encoding the length twice.
+///
+/// (C-not exported) as manual TLV building is not currently supported in bindings
 pub struct WithoutLength<T>(pub T);
 
 impl Writeable for WithoutLength<&String> {