Fix uint64_t compilation errors and implement >64 CPU support

- Add #include <cstdint> to cpu.h, cpu.cpp, and platform.h.in
- Implement extended CpuSet class supporting >64 CPUs
- Add fast path for <=64 CPUs and extended path for >64 CPUs
- Include necessary headers for std::max, std::vector, memset, etc.
- Fix original code's missing stdint.h includes for uint64_t usage
- Maintain backward compatibility with platform-specific APIs

Fixes #6142

src/cpu.cpp

@@ -5,6 +5,7 @@
 
 #include "platform.h"
 
+#include <cstdint>
 #include <limits.h>
 #ifndef __wasi__
 #include <setjmp.h>

src/cpu.h

@@ -5,6 +5,7 @@
 #define NCNN_CPU_H
 
 #include <stddef.h>
+#include <cstdint>
 
 #if defined _WIN32
 #define WIN32_LEAN_AND_MEAN

src/platform.h.in

@@ -4,6 +4,8 @@
 #ifndef NCNN_PLATFORM_H
 #define NCNN_PLATFORM_H
 
+#include <cstdint>
+
 #cmakedefine01 NCNN_STDIO
 #cmakedefine01 NCNN_STRING
 #cmakedefine01 NCNN_SIMPLEOCV