data_transforms dataloader block for automatically RVCing inputs

[bghira]

This pull request adds comprehensive documentation for the new data_transforms feature in the dataloader configuration, across all supported languages. The documentation explains how to use transforms to generate new datasets before normal dataloader setup, with special details on audio identity transfer and the current implementation status.

Key documentation updates:

New data_transforms Section in Dataloader Docs

• Added a new section describing the data_transforms configuration option, including its values, usage, and behavior for expanding source datasets into generated training datasets prior to normal dataloader setup. [1] [2] [3] [4] [5] [6]

Audio Identity Transfer and Implementation Details

• Documented the audio identity transfer transform ({"task": "identity_transfer", "method": "rvc"}) for audio backends, with references to the relevant voice cloning guides in each language. [1] [2] [3] [4] [5] [6]
• Provided information on the current implementation status: transform registry, cache manifest checks, Hub artifact reuse/push, DDP-aware sharding hooks, local RVC logs, and the experimental nature of native RVC training/conversion. [1] [2] [3] [4] [5] [6]

[Copilot]

🔵 Needs a closer look

It changes core factory metadata-clone gating and adds a new audio form flow whose dirty-state/Alpine wiring is only covered by Jest, so human verification and E2E testing are warranted.

Pull request overview

This PR introduces a new data_transforms dataloader block that expands a source dataset into additional generated training datasets before normal dataloader setup, with the first task being audio identity_transfer (RVC-style voice cloning). It wires a new simpletuner/helpers/data_transforms module into the factory, adds a WebUI editor for audio datasets, refactors auto-generated metadata cloning to key off a new metadata_clone_source_id, and adds extensive multilingual documentation. Much of the runtime RVC training/conversion is intentionally scaffolding that raises NotImplementedError; only the cache-reuse path is functional.

Changes:

• New data_transforms registry (base.py) + identity_transfer.py transform, integrated into FactoryRegistry.configure.
• Refactored _handle_bucket_operations to clone metadata via metadata_clone_source_id (set by DatasetDuplicator) instead of auto_generated.
• WebUI support: new audio "Voice Identity Transfer" section, JS helpers, blueprint field; plus EN + zh/ja/pt-BR/es/hi docs.

File summaries

File	Description
simpletuner/helpers/data_transforms/base.py	New DataTransformTask base + registry + process_data_transforms expansion.
simpletuner/helpers/data_transforms/identity_transfer.py	RVC identity-transfer transform, cache/hub/manifest plumbing (training/conversion stubbed).
simpletuner/helpers/data_transforms/init.py	Exposes the registry and transform.
simpletuner/helpers/data_backend/factory.py	Registers process_data_transforms; switches metadata-clone gating to metadata_clone_source_id; versioning keys.
simpletuner/helpers/metadata/utils/duplicator.py	Sets metadata_clone_source_id on generated conditioning configs.
simpletuner/templates/components/dataloader/sections/audio_body.html	New Voice Identity Transfer form section.
simpletuner/templates/trainer_htmx.html	normalizeDataTransforms and save-path handling for audio.
simpletuner/static/js/dataloader-section-component.js	Identity-transfer store helpers + audio-only guards.
simpletuner/simpletuner_sdk/server/data/dataset_blueprints.py	New data_transforms audio blueprint field.
tests/*	Unit/Jest tests for transform, blueprint, and JS helpers.
documentation/*, mkdocs.yml	New Voice Cloning docs + data_transforms DATALOADER entries (all languages).

Review details

• Files reviewed: 32/32 changed files
• Comments generated: 2
• Review effort level: Balanced

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