src: use arithmetic HexEncode instead of lookups

[ChALkeR]

See nodejs/node#61609

This improves Buffer#toString('hex')  2-4x

In local tests on a MacBook, this improves .toString('hex') throughput from ~2.24 GiB/s to ~9.53 GiB/s on ~80 KiB chunks
For comparison, Uint8Array#toHex() shows 3.28 GiB/s.

Benchmark CI: https://ci.nodejs.org/view/Node.js%20benchmark/job/benchmark-node-micro-benchmarks/1790/console

10:57:55                                                 confidence improvement accuracy (*)   (**)  (***)
10:57:55 buffers/buffer-hex-decode.js n=1000000 len=1024        ***    170.96 %       ±1.02% ±1.38% ±1.82%
10:57:55 buffers/buffer-hex-decode.js n=1000000 len=64          ***     53.49 %       ±1.65% ±2.20% ±2.88%
10:57:55 buffers/buffer-hex-encode.js n=1000000 len=1024                 0.13 %       ±0.19% ±0.25% ±0.32%
10:57:55 buffers/buffer-hex-encode.js n=1000000 len=64                  -0.14 %       ±0.85% ±1.13% ±1.47%