Disable cpuinfo on Windows ARM64

[ssss141414]

Summary

• disable the optional cpuinfo integration when targeting native Windows ARM64
• use Ruy's existing conservative cache parameters and platform-based ARM64 path detection

Why

The vendored cpuinfo configuration reports that Windows ARM64 is unsupported and omits the ARM ISA data symbol, while Ruy still defines RUY_HAVE_CPUINFO. Linking an ARM64 consumer then fails with:

ruy_cpuinfo.lib(cpuinfo.obj): error LNK2019: unresolved external symbol cpuinfo_isa referenced in ruy::CpuInfo::NeonDotprod()

Ruy already supports builds without cpuinfo on other platforms. This change limits that existing fallback to Windows ARM64 and leaves all other targets unchanged.

Validation

Validated in a native Windows ARM64 CTranslate2 build using Ruy: the dependency links successfully, INT8 multithreaded inference returns the expected output, and the resulting DLL is native ARM64.

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