Add support for s390x architecture

[ibm-adarsh]

PR introduces support for IBM Z (s390x) architecture in the CPU collector as asked part of #437. Unlike x86 or ARM, s390x provides CPU metadata in a hierarchical format where certain system-wide attributes (like vendor_id and machine) are listed in a header, while individual logical processors are identified by the cpu number key.

Key Changes:

• Parser Update: Modified logicalProcessorsFromProcCPUInfo to recognize cpu number as a valid logical processor identifier (mapping to processor on other architectures).
• Attribute Persistence: Updated the logic to retain attributes collected in the /proc/cpuinfo header. This ensures that vendor_id and machine (Model) metadata are correctly associated with the processor entries rather than being discarded when the parser hits a blank line.
• New Key Mappings: Added support for the features key to populate CPU capabilities on s390x.
• Snapshot Testing: Added a new s390x test snapshot and a corresponding unit test to ensure long-term stability.

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Testing Performed

• Architecture Verified: s390x (IBM z16).

• Unit Tests:
• Added TestS390xCPU in pkg/cpu/cpu_linux_test.go.

• Verified that Vendor reports as IBM/S390 and Model reports the machine type (e.g., 3931).

• Confirmed Capabilities are correctly parsed from the features line.

• Regression Testing:

• Ran existing TestArmCPU and TestCheckCPUTopologyFilesForOfflineCPU on x86/ARM snapshots to ensure no regressions in the standard parsing logic.

• All tests passed: go test -v ./pkg/cpu/...

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Impact

Users running ghw on s390x will now see populated Vendor, Model, and Capabilities fields in the CPUInfo struct, which previously returned empty strings.

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[jaypipes]

Looking good @ibm-adarsh thank you! :)

[jaypipes]

@ibm-adarsh welcome to the ghw contributors club :) thanks again for your efforts here!

[ashokpariya0]

@jaypipes Could we please create a release tag including this change whenever possible?

[jaypipes]

@ashokpariya0 you're all set :) release v0.23.0 includes this patch.

[ashokpariya0]

@ashokpariya0 you're all set :) release v0.23.0 includes this patch.

thanks a lot 👍