Bundle Sender State Machine Rework

[dancoombs]

Closes #362

Proposed Changes

• Remove polling of transaction status from the transaction tracker
• Introduce a new state machine to bundle sender
  • Machine is driven by a "trigger" which depends on the bundling mode and the state
  • Each trigger causes a state update
  • State currently jumps between Building when there are no outstanding bundle transactions, and Pending when there are outstanding transactions.
• Adds handling for nonce too low errors

TODO (in follow up PRs)

• Add a new state to handle "cancellations" where we replace any pending transactions with an empty transaction to fix the "stuck sender" and "replacement underpriced" cases.
• Add tests for the new state machine
• Add support for dropped transactions to certain senders to short circuit pending wait times if dropped.

[dancoombs]

Merged #720 and #721 into this PR.