rust: Make NodePrefix allocation-free and Copy, remove NodePrefixRef The `*Ref` struct only existed to avoid allocating `Vec`s when cloning `NodePrefix`, but we can avoid having `Vec` in the first place by using an inline array instead. This makes `NodePrefix` 21 bytes (with 1?for the length) which is smaller than before as `Vec` alone is 24 bytes. Differential Revision: https://phab.mercurial-scm.org/D9863

--- a/rust/hg-core/src/revlog.rs	Sat Jan 30 18:30:11 2021 +0800
+++ b/rust/hg-core/src/revlog.rs	Mon Jan 25 11:48:47 2021 +0100
@@ -9,7 +9,7 @@
 pub mod nodemap;
 mod nodemap_docket;
 pub mod path_encode;
-pub use node::{FromHexError, Node, NodePrefix, NodePrefixRef};
+pub use node::{FromHexError, Node, NodePrefix};
 pub mod changelog;
 pub mod index;
 pub mod manifest;