2.73.0
(feat): Add opt-in support for a structured User-Agent header on generated SDK
clients of the form {sdkName}/{sdkVersion} ({os}; {arch}) {runtime}/{runtimeVersion}
(e.g. my-sdk/1.2.0 (linux; x64) .NET/8.0.4). The OS, architecture, and
runtime version are resolved at runtime via
System.Runtime.InteropServices.RuntimeInformation and System.Environment.
This is gated behind a new include-platform-headers config option and is
disabled by default, so existing generated output is unchanged. When enabled
it remains subject to the omit-fern-headers config option.