Optimise parsing by removing excessive copying. (#278)

* Optimise parsing by removing excessive copying.

* Add benchmark

---------

Co-authored-by: Joannis Orlandos <joannis@orlandos.nl>

Author: maciejtrybilo

Benchmarks/.vscode/launch.json

@@ -0,0 +1,28 @@
+{
+    "configurations": [
+        {
+            "type": "lldb",
+            "request": "launch",
+            "sourceLanguages": [
+                "swift"
+            ],
+            "args": [],
+            "cwd": "${workspaceFolder:Benchmarks}",
+            "name": "Debug XMLCoderBenchmarks",
+            "program": "${workspaceFolder:Benchmarks}/.build/debug/XMLCoderBenchmarks",
+            "preLaunchTask": "swift: Build Debug XMLCoderBenchmarks"
+        },
+        {
+            "type": "lldb",
+            "request": "launch",
+            "sourceLanguages": [
+                "swift"
+            ],
+            "args": [],
+            "cwd": "${workspaceFolder:Benchmarks}",
+            "name": "Release XMLCoderBenchmarks",
+            "program": "${workspaceFolder:Benchmarks}/.build/release/XMLCoderBenchmarks",
+            "preLaunchTask": "swift: Build Release XMLCoderBenchmarks"
+        }
+    ]
+}

Benchmarks/Benchmarks/XMLCoderBenchmarks/Benchmark.swift

@@ -0,0 +1,14 @@
+import Benchmark
+
+let benchmarks = {
+    Benchmark(
+        "XMLDecoder",
+        configuration: .init(
+            metrics: [
+                .throughput
+            ]
+        )
+    ) { benchmark in
+        try runXMLDecoder()
+    }
+}