feat(messages): add native Anthropic Messages API (/v1/messages)

docs/docs/providers/messages/index.mdx

@@ -0,0 +1,13 @@
+---
+description: "Protocol for the Anthropic Messages API."
+sidebar_label: Messages
+title: Messages
+---
+
+# Messages
+
+## Overview
+
+Protocol for the Anthropic Messages API.
+
+This section contains documentation for all available providers for the **messages** API.

docs/docs/providers/messages/inline_builtin.mdx

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+---
+description: "Anthropic Messages API adapter that translates to the inference API."
+sidebar_label: Builtin
+title: inline::builtin
+---
+
+# inline::builtin
+
+## Description
+
+Anthropic Messages API adapter that translates to the inference API.
+
+## Sample Configuration
+
+```yaml
+{}
+```