Fix future missing_docs lint.

rustc 1.83 will lint `missing_docs` in `--test` builds, which did not
occur previously. <rust-lang/rust#130025>

Author: kpreid

all-is-cubes-desktop/tests/end-to-end.rs

@@ -1,3 +1,5 @@
+//! Tests which execute the `all-is-cubes` binary.
+
 #[test]
 fn trycmd_tests() {
     let tc = trycmd::TestCases::new();

all-is-cubes-port/src/gltf/buffer.rs

@@ -44,7 +44,7 @@ struct Inner {
 
 impl GltfDataDestination {
     #[cfg(test)]
-    pub fn null() -> GltfDataDestination {
+    pub(crate) fn null() -> GltfDataDestination {
         Self(Arc::new(Inner {
             discard: true,
             maximum_inline_length: 0,

all-is-cubes/src/transaction.rs

@@ -14,7 +14,7 @@ pub use generic::*;
 #[cfg(test)]
 mod tester;
 #[cfg(test)]
-pub use tester::*;
+pub(crate) use tester::*;
 
 /// A mutation that is to be performed atomically.
 ///