Calibrate performance benchmarks

[satyakigh]

Description

The required performance check failed before measurement when GitHub scheduled ubuntu-latest on an unrecognized CPU. The latest failure used INTEL(R) XEON(R) PLATINUM 8573C; other recent runs encountered Intel 8370C and AMD EPYC 9V45.

Previously, an unknown CPU caused exit code 2 before any performance results or candidate baseline were written.

This change preserves the hard, two-sided absolute-baseline model:

• Derives deterministic CPU-specific profile names from the detected CPU model.
• Adds an Intel Xeon Platinum 8573C hard baseline using GitHub-hosted runner measurements.
• For an unknown CPU, collects nine independent samples for all 38 cases and uploads:
• performance-results.json
• performance-results.md
• A CPU-enforced performance-candidate-baseline.json
• Keeps the unknown-CPU check failed until its candidate is reviewed and checked in.
• Removes the generic variable-hardware GitHub profile, preventing accidental comparisons between unlike machines.
• Validates every checked-in GitHub profile has the same cases, gates, and thresholds.