feat: implement clear pending txs for go batch submitter

[cfromknecht]

Description
This PR adds logic to the Go Batch Submitter, allowing it to clear any pending transactions from the mempool that may have been left from a prior running instance. It does so by sending a 0-value tx to itself, and waiting until either the transaction confirms or a different transaction at the same nonce has confirmed. After ensuring that the mempool state is in a safe state to proceed, the batch submitter begins operation as before.

In addition, this PR begins the process of mocking out the L1 backend, in a way that can be reused across the project/packages. Continuing this approach will allow us to extensively test for behavior under network-level failures.

Metadata

• Fixes ENG-1887

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⚠️ No Changeset found

Latest commit: 15252dd

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[codecov-commenter]

Codecov Report

Merging #2003 (15252dd) into develop (0f5c810) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #2003   +/-   ##
========================================
  Coverage    74.58%   74.58%           
========================================
  Files           79       79           
  Lines         2554     2554           
  Branches       401      401           
========================================
  Hits          1905     1905           
  Misses         649      649           

Flag	Coverage Δ
batch-submitter	62.50% <ø> (ø)
contracts	90.48% <ø> (ø)
core-utils	57.50% <ø> (ø)
data-transport-layer	38.64% <ø> (ø)
message-relayer	70.86% <ø> (ø)
sdk	88.38% <ø> (ø)

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