fix(node:buffer): honor compare range args

[andrewtdiz]

Part of #793.

Summary

• route buf.compare(target, targetStart?, targetEnd?, sourceStart?, sourceEnd?) through the range-aware helper whenever range args are supplied
• apply Node defaults for omitted/undefined bounds: targetStart=0, targetEnd=target.length, sourceStart=0, sourceEnd=this.length
• preserves the one-argument full-buffer compare path

Verification

• DeepWiki: reference/deepwiki/nodejs-node-buffer-compare-range-args-2026-05-28.md (local only)
• Baseline exact node-suite/buffer/compare/bounds-errors: FAIL, report test-parity/reports/parity_report_20260528_115628.json
• Final exact node-suite/buffer/compare/bounds-errors: PASS, report test-parity/reports/parity_report_20260528_120128.json
• Full granular node-suite/buffer/compare: PASS 2/2, report test-parity/reports/parity_report_20260528_120214.json
• Full granular node-suite/buffer: 104 PASS / 11 parity FAIL / 1 compile FAIL, report test-parity/reports/parity_report_20260528_120221.json; compare/bounds-errors is green. Several sibling reds are covered by open PRs fix(node:buffer): reject negative allocation size #2274/fix(node:buffer): estimate base64 byte length #2276/fix(node:buffer): honor concat total length #2271/fix(node:buffer): expose default iterator #2280/fix(node:buffer): expose inspect surface #2282/fix(node:buffer): reject primitive from inputs #2287 or by separate coercion/range-error work.
• cargo check -p perry-runtime -p perry-stdlib -p perry-codegen: PASS with existing warnings
• cargo fmt --check: PASS
• jq empty test-parity/known_failures.json: PASS
• git diff --check: PASS

Non-goals

• no compare target type validation
• no exact error message text cleanup
• no range-error output cleanup beyond this optional-argument path
• no Buffer.from/write/fill coercion work