Add from_single_file support for SkyReelsV2 and ChronoEdit transformers

[HaozheZhang6]

What does this PR do?

Adds from_single_file support for SkyReelsV2Transformer3DModel and ChronoEditTransformer3DModel so the community GGUF builds (wsbagnsv1's SkyReels-V2, QuantStack's ChronoEdit-14B) load directly.

Both are built on Wan, and their transformers have the same keys as WanTransformer3DModel, so they reuse convert_wan_transformer_to_diffusers — the converter WanVACE and WanAnimate already use.

Ran the conversion against a real GGUF of each (SkyReels-V2-I2V-14B-540P and ChronoEdit-14B, 1303 tensors each): both map onto their model with 0 missing / 0 unexpected / 0 shape mismatch.

Before submitting

• Did you use an AI agent (Claude Code) to help with this PR? Yes.
  • Pointed it at .ai/ — read AGENTS.md and review-rules.md.
  • Self-reviewed the diff against .ai/review-rules.md.
• Did you read the contributor guideline?
• Was this discussed via a GitHub issue? No — follows the existing single_file pattern; happy to open one if you'd prefer.

Who can review?

@DN6

[HuggingFaceDocBuilderDev]

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[github-actions]

Hi @HaozheZhang6, thanks for the PR! It does not appear to link an issue it fixes. If this PR addresses an existing issue, please add a closing keyword (e.g. Fixes #1234) to the PR description so the issue is linked. See the contribution guide for more details. If this PR intentionally does not fix a tracked issue, a maintainer can add the no-issue-needed label to silence this reminder.