feat: Add from_parts and build_split methods to `blocking::Reques…

…tBuilder` struct (#2288)

src/blocking/request.rs

@@ -167,6 +167,14 @@ impl RequestBuilder {
         }
     }
 
+    /// Assemble a builder starting from an existing `Client` and a `Request`.
+    pub fn from_parts(client: Client, request: Request) -> RequestBuilder {
+        RequestBuilder {
+            client,
+            request: crate::Result::Ok(request),
+        }
+    }
+
     /// Add a `Header` to this Request.
     ///
     /// ```rust
@@ -550,6 +558,15 @@ impl RequestBuilder {
         self.request
     }
 
+    /// Build a `Request`, which can be inspected, modified and executed with
+    /// `Client::execute()`.
+    ///
+    /// This is similar to [`RequestBuilder::build()`], but also returns the
+    /// embedded `Client`.
+    pub fn build_split(self) -> (Client, crate::Result<Request>) {
+        (self.client, self.request)
+    }
+
     /// Constructs the Request and sends it the target URL, returning a Response.
     ///
     /// # Errors