Add encode_descriptor and encode_metric

Author: patrick-ogrady

CHANGELOG.md

@@ -4,6 +4,15 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Added
+
+- Added `encoding::text::encode_descriptor` and `encoding::text::encode_metric`
+  for custom registries that need to compose descriptors, samples and EOF
+  markers independently.
+- Added `EncodeMetric` forwarding for `Arc<T: EncodeMetric>`.
+
 ## [0.24.1]
 
 ### Added

src/encoding.rs

@@ -71,6 +71,24 @@ impl EncodeMetric for Box<dyn EncodeMetric> {
     fn metric_type(&self) -> MetricType {
         self.deref().metric_type()
     }
+
+    fn is_empty(&self) -> bool {
+        self.deref().is_empty()
+    }
+}
+
+impl<T: EncodeMetric + ?Sized> EncodeMetric for Arc<T> {
+    fn encode(&self, encoder: MetricEncoder) -> Result<(), std::fmt::Error> {
+        self.deref().encode(encoder)
+    }
+
+    fn metric_type(&self) -> MetricType {
+        self.deref().metric_type()
+    }
+
+    fn is_empty(&self) -> bool {
+        self.deref().is_empty()
+    }
 }
 
 /// Encoder for a Metric Descriptor.