fix(hz/protobuf): preserve api.body custom name for oneof wrapper fields

[WyRainBow]

Summary

• replace internal_gengo oneof wrapper generation with a hertz implementation that applies injectTagsToStructTags to oneof choice fields
• keep existing protobuf tags while injecting hertz binding/json/form tags from field options

Fixes #1474

[WyRainBow]

Added a targeted fix for oneof wrappers so choice fields also receive hertz tag injection (injectTagsToStructTags).

This makes (api.body)="..." effective for oneof choices in generated Go code (json/form tags no longer fall back to field GoName).

Regression coverage included in TestOneofFieldCustomBodyTag with dedicated test proto/request fixtures.

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[xiaost]

Hi, we have no plan to support any new feature now.