feat: add C ABI, Python package, and CPU ISA paths

Expose the PP-OCRv6 engine through a stable C ABI and installable
shared and static libraries, plus a ctypes Python package that follows
the RapidOCR call shape. Keep AVX-512 out of the AVX2 object file and
speed up GEMM accumulate and the AArch64 GEMM tile.

Co-authored-by: Daniel <znsoft@163.com>

examples/cpp_api_demo.cpp

@@ -0,0 +1,37 @@
+#include "ppocr/ppocr.hpp"
+
+#include <iostream>
+#include <string>
+
+int main(int argc, char** argv) {
+  const auto cpu = ppocr::QueryCpuInfo();
+  if (argc == 2 && std::string(argv[1]) == "--cpu-info") {
+    std::cout << "active_isa=" << cpu.active_isa
+              << " avx2=" << cpu.avx2
+              << " avx512=" << cpu.avx512
+              << " neon=" << cpu.neon
+              << " threads=" << cpu.threads << '\n';
+    return 0;
+  }
+  if (argc != 5) {
+    std::cerr << "usage: ppocr_cpp_api_demo DET.onnx REC.onnx dict.txt image.ppm\n";
+    return 2;
+  }
+  try {
+    ppocr::Options options;
+    options.backend = ppocr::Backend::cpu_only;
+    ppocr::OCR ocr(argv[1], argv[2], argv[3], options);
+    const ppocr::Image image = ppocr::LoadPPM(argv[4]);
+    const auto results = ocr.Recognize(image);
+    std::cout << "isa=" << cpu.active_isa << " boxes=" << results.size() << '\n';
+    for (const auto& result : results) {
+      std::cout << result.text << '\t' << result.confidence << '\t'
+                << result.bbox[0] << ',' << result.bbox[1] << ','
+                << result.bbox[2] << ',' << result.bbox[3] << '\n';
+    }
+  } catch (const std::exception& ex) {
+    std::cerr << "error: " << ex.what() << '\n';
+    return 1;
+  }
+  return 0;
+}