* fix: track challenges when pipeline is stalled

* cleanup

* fix: remove tx version byte in test

* remove Heap usage

* fix: add pending queue

* remove unused check

* use 2 PQs

* Update comment in op-e2e/actions/plasma_test.go
Co-authored-by: Joshua Gutow <jbgutow@gmail.com>

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Co-authored-by: Joshua Gutow <jbgutow@gmail.com>