feat: Add git_odb_backend_data_malloc and git_odb_backend_data_free

Added `git_odb_backend_data_malloc` and `git_odb_backend_data_free`.

Deprecated `git_odb_backend_malloc` in favour of the above two functions
as it has been deprecated for over 6 years.

Author: tecc

libgit2-sys/lib.rs

@@ -4115,15 +4115,20 @@ extern "C" {
         priority: c_int,
     ) -> c_int;
 
+    #[deprecated(note = "only kept for compatibility; prefer git_odb_backend_data_alloc")]
     pub fn git_odb_backend_malloc(backend: *mut git_odb_backend, len: size_t) -> *mut c_void;
 
+    pub fn git_odb_backend_data_alloc(backend: *mut git_odb_backend, len: size_t) -> *mut c_void;
+    pub fn git_odb_backend_data_free(backend: *mut git_odb_backend, data: *mut c_void);
+
     pub fn git_odb_num_backends(odb: *mut git_odb) -> size_t;
     pub fn git_odb_get_backend(
         backend: *mut *mut git_odb_backend,
         odb: *mut git_odb,
         position: size_t,
     ) -> c_int;
 
+
     // mempack
     pub fn git_mempack_new(out: *mut *mut git_odb_backend) -> c_int;
     pub fn git_mempack_reset(backend: *mut git_odb_backend) -> c_int;