rust-index: add Sync bound to all relevant mmap-derived values

All readonly mmaps are Sync as far as Rust is concerned. Integrity of the
mmap'ed file is a concern separate to Rust's memory model, since it requires
out-of-program handling via locks, etc.

This will help when we start sharing the Rust Index with Python.

rust/hg-core/src/revlog/index.rs

@@ -85,7 +85,7 b' impl IndexHeader {'
 /// happened. This makes it transparent for the callers.
 struct IndexData {
     /// Immutable bytes, most likely taken from disk
-    bytes: Box<dyn Deref<Target = [u8]> + Send>,
+    bytes: Box<dyn Deref<Target = [u8]> + Send + Sync>,
     /// Used when stripping index contents, keeps track of the start of the
     /// first stripped revision, which is used to give a slice of the
     /// `bytes` field.
@@ -95,7 +95,7 b' struct IndexData {'
 }
 
 impl IndexData {
-    pub fn new(bytes: Box<dyn Deref<Target = [u8]> + Send>) -> Self {
+    pub fn new(bytes: Box<dyn Deref<Target = [u8]> + Send + Sync>) -> Self {
         Self {
             bytes,
             truncation: None,
@@ -328,7 +328,7 b' impl Index {'
     /// Create an index from bytes.
     /// Calculate the start of each entry when is_inline is true.
     pub fn new(
-        bytes: Box<dyn Deref<Target = [u8]> + Send>,
+        bytes: Box<dyn Deref<Target = [u8]> + Send + Sync>,
         default_header: IndexHeader,
     ) -> Result<Self, HgError> {
         let header =

rust/hg-cpython/src/revlog.rs

@@ -520,7 +520,7 b' unsafe fn mmap_keeparound('
     data: PyObject,
 ) -> PyResult<(
     PyBuffer,
-    Box<dyn std::ops::Deref<Target = [u8]> + Send + 'static>,
+    Box<dyn std::ops::Deref<Target = [u8]> + Send + Sync + 'static>,
 )> {
     let buf = PyBuffer::get(py, &data)?;
     let len = buf.item_count();