Support offset value v4

[justin-chen]

Similar to: #472
OffsetCommitValue V4: apache/kafka#19683

For compatibility with Kafka 4.1.0, add decodeOffsetValueV4. Fixes decoding errors such as:

{
  "level": "warn",
  "ts": 1759190908.5072575,
  "msg": "failed to decode",
  "type": "module",
  "coordinator": "consumer",
  "class": "kafka",
  "name": "kafka-staging-us-east1-consumers",
  "offset_topic": "__consumer_offsets",
  "offset_partition": 31,
  "offset_offset": 120351075,
  "message_type": "offset",
  "group": "kafka-client-go-test-staging",
  "topic": "kafka_client_go_test",
  "partition": 1,
  "offset": 4025888141,
  "timestamp": 0,
  "reason": "metadata"
}

By decoding offset value metadata using compact string, we determine string length by reading with uint8 rather than int16, which should be the default:

COMPACT_STRING | Represents a sequence of characters. First the length N + 1 is given as an UNSIGNED_VARINT . Then N bytes follow which are the UTF-8 encoding of the character sequence.

[justin-chen]

Addressed lint errors by adding constants for the errors.

[bai]

You rock! Thanks for your contribution!