Include every Windows processor when counting physical cores

[OskarEichler]

Summary

The WMI query returns one row per physical processor, but cpu_count only reads the first row. Sum NumberOfCores across all rows, retaining the existing physical-core meaning.

Reproduction and verification

Checked one-, two- and three-processor WMI fixtures, including unequal core counts. Native Windows/WMI execution remains for upstream CI; local checks use stubs.

• External focused repro corpus: 5 checks pass against this isolated branch, under rbenv Ruby 4.0.6.
• Existing upstream suite: 36 examples, zero failures before and after the patch (RBENV_VERSION=4.0.6 rbenv exec rspec -Ilib -Ispec).
• Source-only change; no existing tests modified or new test files added, per the contributor's task constraint. The focused corpus lives outside the repository.
• Local verification was on macOS. Other Ruby versions and native operating systems were not executed. Upstream RuboCop configuration cannot load its legacy rubocop-lts1_8.yml, including after installing current rubocop-lts; lint status is not represented as passing.

Breaking-change notes

No API removal. Multi-socket Windows machines report the total physical cores instead of only the first socket. Logical/hyperthread count semantics are unchanged.