Introduce CompactedKeyEncoder

[luoyuxia]

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• I searched in the issues and found nothing similar.

Description

as title. Please refer to java implementation https://github.com/search?q=repo%3Aapache%2Ffluss%20CompactedKeyEncoder&type=code

Willingness to contribute

• I'm willing to submit a PR!

[luoyuxia]

Blocked by #118

[luoyuxia]

@leekeiabstraction Since #118 is finished, and you already take #113 which is blocked by this issue. Do you want to take this issue as well?

[luoyuxia]

Let's just consider default key encoder and don't support iceberg & paimon currently.

[leekeiabstraction]

@luoyuxia yes happy to take this as I'm already working on this