fix(node:buffer): reject negative allocation size

[andrewtdiz]

Summary:

• Throw RangeError with ERR_OUT_OF_RANGE for negative Buffer allocation sizes.
• Apply the check before Buffer.alloc, filled Buffer.alloc, and Buffer.allocUnsafe allocation paths.
• Buffer.allocUnsafeSlow shares the unsafe allocation helper, so it gets the same validation.

Part of #793.

Evidence:

• Baseline exact ./run_parity_tests.sh --suite node-suite --filter node-suite/buffer/allocation/alloc-fill-typedarray: FAIL, report test-parity/reports/parity_report_20260528_104915.json.
• Final exact ./run_parity_tests.sh --suite node-suite --filter node-suite/buffer/allocation/alloc-fill-typedarray: PASS, report test-parity/reports/parity_report_20260528_105240.json.
• Allocation subgroup ./run_parity_tests.sh --suite node-suite --module buffer/allocation: PASS 9/9, report test-parity/reports/parity_report_20260528_105327.json.
• Full granular ./run_parity_tests.sh --suite node-suite --module buffer: 104 PASS / 11 parity FAIL / 1 compile FAIL, report test-parity/reports/parity_report_20260528_105340.json; allocation is green. buffer/concat/edge-lengths remains red on this branch because it is fixed separately in open PR fix(node:buffer): honor concat total length #2271. Other residuals remain in byteLength edge encodings, compare bounds, fill/write coercions, Buffer.from coercions/errors, inspect limits, iterator, range-error edge cases, and ucs2 search compile behavior.
• 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.

DeepWiki:

• Local-only reference: reference/deepwiki/nodejs-node-buffer-alloc-negative-size-2026-05-28.md.

Non-goals:

• No maximum allocation length validation.
• No non-integer size coercion cleanup.
• No Uint8Array/ArrayBuffer constructor validation.
• No adjacent Buffer.from/write/fill coercion work.