T5 export failure

[jackzhxng]

See error trace here - https://github.com/huggingface/optimum-executorch/actions/runs/16994343556/job/48181308316?pr=117.

Should affect all seq2seq models such as Whisper - the transformers bump introduces at least two problems to deal with:

• is_updated not initialized outside of if statement
  • Fix is potentially a transformers upstream
• The cache not being a EncoderDecoderCache, since we use Seq2SeqLMDecoderExportableModuleWithStaticCache to export the decoder
  • Fix is to add a new class Seq2SeqLMDecoderExportableModuleWithEncoderDecoderCache that has a self attention and cross attention cache

[jowunnal]

Hi @jackzhxng , I face these issues while I was exporting whisper model to .pte. Is there any progress on these issue?

[jackzhxng]

Hi @jowunnal, thanks for your patience. This will be fixed in #146