Fix jemalloc warning on macOS (#1344)

fix:
```
-> % easytier-core
<jemalloc>: option background_thread currently supports pthread only
```

Reference: https://github.com/apache/arrow/pull/5729

easytier/Cargo.toml

@@ -258,11 +258,17 @@ jemallocator = { package = "tikv-jemallocator", version = "0.6.0", optional = tr
 ] }
 jemalloc-ctl = { package = "tikv-jemalloc-ctl", version = "0.6.0", optional = true, features = [
 ] }
+
+[target.'cfg(not(target_os = "macos"))'.dependencies]
 jemalloc-sys = { package = "tikv-jemalloc-sys", version = "0.6.0", features = [
     "background_threads_runtime_support",
     "background_threads",
 ], optional = true }
 
+[target.'cfg(target_os = "macos")'.dependencies]
+jemalloc-sys = { package = "tikv-jemalloc-sys", version = "0.6.0", features = [
+], optional = true }
+
 [build-dependencies]
 tonic-build = "0.12"
 globwalk = "0.8.1"