feat!: Add #[non_exhaustive] to ChangeSet structs in tx_graph, keychain_txout, local_chain

Add #[non_exhaustive] attribute to the ChangeSet structs to prevent downstream
crates from exhaustively matching or constructing instances using struct
literal syntax, allowing future additions without breaking compatibility.

The change improves forward compatibility by allowing new fields to be added
without breaking downstream code in future releases.

Author: notmandatory

crates/chain/src/indexer/keychain_txout.rs

@@ -1021,6 +1021,7 @@ impl<K: core::fmt::Debug> std::error::Error for InsertDescriptorError<K> {}
 #[derive(Clone, Debug, Default, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 #[must_use]
+#[non_exhaustive]
 pub struct ChangeSet {
     /// Maps each `DescriptorId` to its last revealed derivation index.
     pub last_revealed: BTreeMap<DescriptorId, u32>,

crates/chain/src/local_chain.rs

@@ -408,6 +408,7 @@ impl LocalChain {
 /// The [`ChangeSet`] represents changes to [`LocalChain`].
 #[derive(Debug, Default, Clone, PartialEq)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[non_exhaustive]
 pub struct ChangeSet {
     /// Changes to the [`LocalChain`] blocks.
     ///

crates/chain/src/tx_graph.rs

@@ -173,6 +173,7 @@ impl<A: Anchor> From<TxUpdate<A>> for TxGraph<A> {
 ///
 /// [module-level documentation]: crate::tx_graph
 #[derive(Clone, Debug, PartialEq)]
+#[non_exhaustive]
 pub struct TxGraph<A = ConfirmationBlockTime> {
     txs: HashMap<Txid, TxNodeInternal>,
     spends: BTreeMap<OutPoint, HashSet<Txid>>,
@@ -1415,6 +1416,7 @@ impl<A: Anchor> TxGraph<A> {
     ))
 )]
 #[must_use]
+#[non_exhaustive]
 pub struct ChangeSet<A = ()> {
     /// Added transactions.
     pub txs: BTreeSet<Arc<Transaction>>,