Support Keras 3 models in from_keras

[nfirle]

Summary

This PR adds support for Keras 3 in the from_keras conversion function. Keras 3 introduced several breaking changes in model serialization and internal APIs, which caused the existing conversion logic to fail. This update ensures compatibility with the new format.

Changes

• Added a new function from_keras3 that handles models created with Keras 3.
• Updated from_keras to detect the Keras version and delegate to from_keras3 when necessary.
• The from_keras3 function is designed to also work with older Keras versions, but for full backward compatibility, the original from_keras logic is preserved.
• This approach minimizes the risk of regressions and keeps the behavior consistent for users still relying on Keras 2.