Co-authored-by: JzoNg <jzongcode@gmail.com>

Co-authored-by: 刘江波 <jiangbo721@163.com>

Co-authored-by: Yeuoly <45712896+Yeuoly@users.noreply.github.com>

Co-authored-by: zxhlyh <jasonapring2015@outlook.com>
Co-authored-by: Yeuoly <admin@srmxy.cn>

Co-authored-by: crazywoola <100913391+crazywoola@users.noreply.github.com>

Co-authored-by: JzoNgKVO <27049666+JzoNgKVO@users.noreply.github.com>

Co-authored-by: NFish <douxc512@gmail.com>
Co-authored-by: JzoNg <jzongcode@gmail.com>
Co-authored-by: Garfield Dai <dai.hai@foxmail.com>

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Co-authored-by: Novice <novice12185727@gmail.com>

refactor(api): Separate SegmentType for Integer/Float to Enable Pydantic Serialization (#22025)

This PR addresses serialization issues in the VariablePool model by separating the `value_type` tags for `IntegerSegment`/`FloatSegment` and `IntegerVariable`/`FloatVariable`. Previously, both Integer and Float types shared the same `SegmentType.NUMBER` tag, causing conflicts during serialization.

Key changes:
- Introduce distinct `value_type` tags for Integer and Float segments/variables
- Add `VariableUnion` and `SegmentUnion` types for proper type discrimination
- Leverage Pydantic's discriminated union feature for seamless serialization/deserialization
- Enable accurate serialization of data structures containing these types

Closes #22024.

Co-authored-by: crazywoola <100913391+crazywoola@users.noreply.github.com>
Co-authored-by: crazywoola <427733928@qq.com>