[CB] Fix capture of max_seqlen (#45323)
* Fine-grained control over varlen and decode path for CGs
* Add padding for max_seqlen
* Add max_seqlen to the key
* Fix padding
* Style
* Fix logits processors and compile
* Remove the compile disabling for varlen path
* Add tests for fa3
* Fix bug and disable varlen compile
* Adapted checks for the new tuple behavior
* Fixing tests
* Style
* restrict kwargs
* Review compliance
