feat(nori): add metadata support to Korean tokenizer

[twosom]

Description

Summary

Adds metadata support to Nori Korean analyzer, allowing users to attach additional information to dictionary words.

Changes

• Added MetadataAttribute interface and implementation
• Extended user dictionary format to support word >> metadata syntax
• Preserves metadata during compound word decomposition
• Maintains backward compatibility with existing dictionaries

Example

Dictionary:

자바 >> computer language
엘라스틱서치 엘라스틱 서치 >> search engine

Result:

• 자바 → Term: "자바", Metadata: "computer language"
• 엘라스틱서치 → All decomposed terms ("엘라스틱서치", "엘라스틱", "서치") carry "search engine" metadata

Fixes #14940

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