support cpu count > 64

[JaredforReal]

Fix: #6142 support cpu count > 64

---

对于Win平台：
使用多组掩码方案，每组默认为64。根据Windows系统版本设置最大CPU支持数
生产环境中，group = 1（cpu count <= 64）的情况下，使用legacy mode，保留原始逻辑

缺憾：在group > 1（cpu count > 64)的情况下，假定了每组的性能以及功能相同，未区分大小核

新增单元测试：test_multicpu，在测试环境中，屏蔽 legacy mode 强制使用 group 逻辑，验证多组掩码的逻辑功能

对于Linux/Android平台：
未作修改。
cpu_set_t 的大小，在现代主流实现（如 glibc）默认通过 CPU_SETSIZE 定义为 ​1024。即原生支持 cpu count > 64 如想支持 > 1024，可使用 cpu_set_t* 加上带有_S POSIX指令实现

对于Apple平台：
未作修改。
unsigned int 最高支持32核，考虑到Apple目前没有超过32核的芯片，为了面向未来的健壮性，可改用 uint64_t以支持64 cpu

其余单元测试结果与主分支一致

修改文件
src/cpu.cpp
src/cpu.h
tests/CMakeList.txt

新增文件
tests/test_multicpu.cpp

[tencent-adm]

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[github-actions]

The binary size change of libncnn.so (bytes)

architecture	base size	pr size	difference
x86_64	15631136	15631136	0 😘
armhf	6635836	6635836	0 😘
aarch64	9987672	9987672	0 😘

[github-actions]

Please enable github action in YOUR FORKED REPO to make code-format workflow work

[JaredforReal]

get rid of legacy mode to keep consistency and reduce compelxity. Functionality remains unchanged, and unit test results are consistent with the master branch
去掉了 legacy mode 来保证一致性和降低复杂度。功能不变，单元测试结果与master branch一致

[JaredforReal]

try fix cross-platform compilation error
尝试解决跨平台编译错误问题

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.05%. Comparing base (6c44404) to head (d8d0d38).
Report is 4 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #6189       +/-   ##
===========================================
- Coverage   95.78%   94.05%    -1.74%     
===========================================
  Files         835      417      -418     
  Lines      252528   120537   -131991     
===========================================
- Hits       241887   113371   -128516     
+ Misses      10641     7166     -3475     

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