add new_with_weight

---
use weight as param
---
fix format and doc comment
---
add ext as Extensions::new
---
Merge branch 'main' into ~~~

Includes-commit: 0d4a658cf8
Includes-commit: 1ee9b327b4
Includes-commit: 5b05294e24
Includes-commit: cf8faea7d0
Includes-commit: f0cefff7eb
Replicated-from: https://github.com/cloudflare/pingora/pull/333

.bleep

@@ -1 +1 @@
-c02dc12f1f7caf9aa90a13112321cf5c3d2f6b6d
+f6e596e897d73c69369ae85edf58cec64b106969

pingora-load-balancing/src/lib.rs

@@ -77,12 +77,18 @@ impl Backend {
     /// Create a new [Backend] with `weight` 1. The function will try to parse
     ///  `addr` into a [std::net::SocketAddr].
     pub fn new(addr: &str) -> Result<Self> {
+        Self::new_with_weight(addr, 1)
+    }
+
+    /// Creates a new [Backend] with the specified `weight`. The function will try to parse
+    /// `addr` into a [std::net::SocketAddr].
+    pub fn new_with_weight(addr: &str, weight: usize) -> Result<Self> {
         let addr = addr
             .parse()
             .or_err(ErrorType::InternalError, "invalid socket addr")?;
         Ok(Backend {
             addr: SocketAddr::Inet(addr),
-            weight: 1,
+            weight,
             ext: Extensions::new(),
         })
         // TODO: UDS