RAGFlow go API server (#13240)

# RAGFlow Go Implementation Plan 🚀

This repository tracks the progress of porting RAGFlow to Go. We'll
implement core features and provide performance comparisons between
Python and Go versions.

## Implementation Checklist

- [x] User Management APIs
- [x] Dataset Management Operations
- [x] Retrieval Test
- [x] Chat Management Operations
- [x] Infinity Go SDK

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>
Co-authored-by: Yingfeng Zhang <yingfeng.zhang@gmail.com>

internal/cpp/util/mix.h

@@ -0,0 +1,41 @@
+// Copyright 2016 The RE2 Authors.  All Rights Reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#ifndef UTIL_MIX_H_
+#define UTIL_MIX_H_
+
+#include <limits>
+#include <stddef.h>
+
+namespace re2 {
+
+// Silence "truncation of constant value" warning for kMul in 32-bit mode.
+// Since this is a header file, push and then pop to limit the scope.
+#ifdef _MSC_VER
+#pragma warning(push)
+#pragma warning(disable : 4309)
+#endif
+
+class HashMix {
+public:
+    HashMix() : hash_(1) {}
+    explicit HashMix(size_t val) : hash_(val + 83) {}
+    void Mix(size_t val) {
+        static const size_t kMul = static_cast<size_t>(0xdc3eb94af8ab4c93ULL);
+        hash_ *= kMul;
+        hash_ = ((hash_ << 19) | (hash_ >> (std::numeric_limits<size_t>::digits - 19))) + val;
+    }
+    size_t get() const { return hash_; }
+
+private:
+    size_t hash_;
+};
+
+#ifdef _MSC_VER
+#pragma warning(pop)
+#endif
+
+} // namespace re2
+
+#endif // UTIL_MIX_H_