fix(node:os): return CPU info shape

[andrewtdiz]

Summary

• replace the empty os.cpus() runtime stub with Node-shaped CPU info objects
• populate model, speed, and nested times.{user,nice,sys,idle,irq} fields
• use Linux /proc/cpufreq data when available and a shape-compatible available-parallelism fallback elsewhere

Before

• ./run_parity_tests.sh --suite node-suite --module os --filter loadavg-and-cpus-shape failed because Perry returned an empty os.cpus() array, so the first CPU field-shape line was missing.

Verification

• cargo fmt --all --check
• cargo check -p perry-runtime
• ./scripts/check_file_size.sh
• ./scripts/regen_api_docs.sh (no docs diff)
• git diff --check
• ./run_parity_tests.sh --suite node-suite --module os --filter loadavg-and-cpus-shape
• ./run_parity_tests.sh --suite node-suite --module os --filter cpus (2/2 pass)
• ./run_parity_tests.sh --suite node-suite --module os --filter platform (5/5 pass)
• ./run_parity_tests.sh --suite node-suite --module os (34 pass / 5 unrelated fail)

Reference

Non-goals

• os.networkInterfaces() address entry shape
• os.getPriority() / os.setPriority() (covered separately by fix(node:os): add priority methods #1892)
• os.devNull string-property method lowering (covered separately by fix(node:os): treat string constants as value method receivers #1890)
• os.constants identity (covered separately by fix(node:os): stabilize constants namespace identity #1887)
• os.userInfo({ encoding: "buffer" }) (covered separately by fix(node:os): return buffers for userInfo buffer encoding #1884)

Closes #793
Refs #800