Update to go-m1cpu 0.2.1 to avoid M5 segfault

[netshade]

When running cirrus on an M5 CPU, the program segfaults immediately:

SIGSEGV: segmentation violation
PC=0x18db1b1a8 m=0 sigcode=2 addr=0x0
signal arrived during cgo execution

goroutine 1 gp=0x140000021c0 m=0 mp=0x106f57020 [syscall, locked to thread]:
runtime.cgocall(0x105b6e960, 0x140000a6e08)
        /opt/homebrew/Cellar/go/1.25.5/libexec/src/runtime/cgocall.go:167 +0x44 fp=0x140000a6dd0 sp=0x140000a6d90 pc=0x104da39d4
github.com/shoenig/go-m1cpu._Cfunc_initialize()
        _cgo_gotypes.go:150 +0x2c fp=0x140000a6e00 sp=0x140000a6dd0 pc=0x105472a7c
github.com/shoenig/go-m1cpu.init.0()
        /Users/admin/go/pkg/mod/github.com/shoenig/go-m1cpu@v0.1.6/cpu.go:148 +0x1c fp=0x140000a6e10 sp=0x140000a6e00 pc=0x105472abc
runtime.doInit1(0x106e82040)
        /opt/homebrew/Cellar/go/1.25.5/libexec/src/runtime/proc.go:7670 +0xc4 fp=0x140000a6f40 sp=0x140000a6e10 pc=0x104d834f4
runtime.doInit(...)
        /opt/homebrew/Cellar/go/1.25.5/libexec/src/runtime/proc.go:7637
runtime.main()
        /opt/homebrew/Cellar/go/1.25.5/libexec/src/runtime/proc.go:256 +0x338 fp=0x140000a6fd0 sp=0x140000a6f40 pc=0x104d73668
runtime.goexit({})
        /opt/homebrew/Cellar/go/1.25.5/libexec/src/runtime/asm_arm64.s:1268 +0x4 fp=0x140000a6fd0 sp=0x140000a6fd0 pc=0x104daf024

It appears that this is caused by a bug in go-m1cpu that has been fixed in 0.2.1. This PR updates the dependency to prevent the segfault and allow running the binary.

Tested and confirmed on an M5 CPU.

[iamszabo]

I'm also experiencing the same issue on M5 Pro while trying to install it with homebrew.

[iamszabo]

@fkorotkov Would it be possible to merge this PR? Without this PR it's not possible to run cirrus on new MacBooks