fix(alloc): potentially dangling temporary (#772)

* fix: potentially dangling temporary

I was trying out the Rust 2024 edition which required a new nightly.
There's now a warning for dangling_pointers_from_temporaries. This
could be a false positive but I am not certain.

* test: skip problematic miri tests on MacOS

These are all due to kqueue, example:

```
error: unsupported operation: can't call foreign function `kqueue` on OS `macos`
   --> /levi.morrison/.cargo/registry/src/index.crates.io-6f17d22bba15001f/mio-1.0.2/src/sys/unix/selector/kqueue.rs:76:48
    |
76  |         let kq = unsafe { OwnedFd::from_raw_fd(syscall!(kqueue())?) };
    |                                                ^^^^^^^^^^^^^^^^^^ can't call foreign function `kqueue` on OS `macos`
```

* test: fix env test when running locally

If the local env has this set, it fails.

alloc/src/chain.rs

@@ -288,10 +288,9 @@ impl<A: Allocator + Clone> Drop for ChainAllocator<A> {
                     // moved to the stack before the chunk is dropped, so it's
                     // alive and valid after the chunk is dropped below.
                     chain_node_ptr = unsafe {
-                        core::ptr::addr_of!((*non_null.as_ptr()).prev)
-                            .read()
-                            .get()
-                            .read()
+                        // Save to variable to avoid a dangling temporary.
+                        let unsafe_cell = core::ptr::addr_of!((*non_null.as_ptr()).prev).read();
+                        unsafe_cell.get().read()
                     };
 
                     // SAFETY: the chunk hasn't been dropped yet, and the

data-pipeline/src/trace_exporter.rs

@@ -918,6 +918,7 @@ mod tests {
     use tinybytes::BytesString;
     use tokio::time::sleep;
 
+    #[cfg_attr(all(miri, target_os = "macos"), ignore)]
     #[test]
     fn new() {
         let builder = TraceExporterBuilder::default();
@@ -951,6 +952,7 @@ mod tests {
         assert!(!exporter.metadata.client_computed_stats);
     }
 
+    #[cfg_attr(all(miri, target_os = "macos"), ignore)]
     #[test]
     fn new_defaults() {
         let builder = TraceExporterBuilder::default();

sidecar/src/service/debugger_diagnostics_bookkeeper.rs

@@ -172,6 +172,7 @@ mod tests {
         }
     }
 
+    #[cfg_attr(all(miri, target_os = "macos"), ignore)]
     #[tokio::test]
     async fn test_bookkeeper() {
         let bookkeeper = DebuggerDiagnosticsBookkeeper::start();

sidecar/src/service/session_info.rs

@@ -308,6 +308,7 @@ mod tests {
     use super::*;
 
     #[tokio::test]
+    #[cfg_attr(all(miri, target_os = "macos"), ignore)]
     async fn test_get_runtime() {
         let session_info = SessionInfo::default();
         let runtime_id = "runtime1".to_string();

trace-mini-agent/src/config.rs

@@ -122,6 +122,7 @@ mod tests {
     #[test]
     #[serial]
     fn test_error_if_no_api_key_env_var() {
+        env::remove_var("DD_API_KEY");
         let config = config::Config::new();
         assert!(config.is_err());
         assert_eq!(

trace-protobuf/src/pb_test.rs

@@ -36,6 +36,7 @@ mod tests {
 
     use crate::pb::{ClientGroupedStats, ClientStatsBucket, ClientStatsPayload, Trilean::NotSet};
 
+    #[cfg_attr(all(miri, target_os = "macos"), ignore)]
     #[tokio::test]
     async fn test_deserialize_client_stats_payload() {
         let stats_json = r#"{

trace-utils/src/stats_utils.rs

@@ -85,6 +85,7 @@ mod tests {
     use serde_json::Value;
 
     #[tokio::test]
+    #[cfg_attr(all(miri, target_os = "macos"), ignore)]
     async fn test_get_stats_from_request_body() {
         let stats_json = r#"{
             "Hostname": "TestHost",
@@ -188,6 +189,7 @@ mod tests {
     }
 
     #[tokio::test]
+    #[cfg_attr(all(miri, target_os = "macos"), ignore)]
     async fn test_get_stats_from_request_body_without_stats() {
         let stats_json = r#"{
             "Hostname": "TestHost",
@@ -239,6 +241,7 @@ mod tests {
     }
 
     #[tokio::test]
+    #[cfg_attr(all(miri, target_os = "macos"), ignore)]
     async fn test_serialize_client_stats_payload_without_stats() {
         let client_stats_payload_without_stats = ClientStatsPayload {
             hostname: "TestHost".to_string(),

trace-utils/src/trace_utils.rs

@@ -743,6 +743,7 @@ mod tests {
 
     #[tokio::test]
     #[allow(clippy::type_complexity)]
+    #[cfg_attr(all(miri, target_os = "macos"), ignore)]
     async fn get_v05_traces_from_request_body() {
         let data: (
             Vec<String>,