feat(translator): add built-in translator registry and helpers

- Introduced `builtin` package exposing a default registry and pipeline for built-in translators.
- Added format constants for common schemas (e.g., OpenAI, Gemini, Codex).
- Implemented helper functions for schema translation using format name strings.
- Provided example usage for integration with translator helpers.

sdk/translator/helpers.go

@@ -0,0 +1,28 @@
+package translator
+
+import "context"
+
+// TranslateRequestByFormatName converts a request payload between schemas by their string identifiers.
+func TranslateRequestByFormatName(from, to Format, model string, rawJSON []byte, stream bool) []byte {
+	return TranslateRequest(from, to, model, rawJSON, stream)
+}
+
+// HasResponseTransformerByFormatName reports whether a response translator exists between two schemas.
+func HasResponseTransformerByFormatName(from, to Format) bool {
+	return HasResponseTransformer(from, to)
+}
+
+// TranslateStreamByFormatName converts streaming responses between schemas by their string identifiers.
+func TranslateStreamByFormatName(ctx context.Context, from, to Format, model string, originalRequestRawJSON, requestRawJSON, rawJSON []byte, param *any) []string {
+	return TranslateStream(ctx, from, to, model, originalRequestRawJSON, requestRawJSON, rawJSON, param)
+}
+
+// TranslateNonStreamByFormatName converts non-streaming responses between schemas by their string identifiers.
+func TranslateNonStreamByFormatName(ctx context.Context, from, to Format, model string, originalRequestRawJSON, requestRawJSON, rawJSON []byte, param *any) string {
+	return TranslateNonStream(ctx, from, to, model, originalRequestRawJSON, requestRawJSON, rawJSON, param)
+}
+
+// TranslateTokenCountByFormatName converts token counts between schemas by their string identifiers.
+func TranslateTokenCountByFormatName(ctx context.Context, from, to Format, count int64, rawJSON []byte) string {
+	return TranslateTokenCount(ctx, from, to, count, rawJSON)
+}