Closes #550

Proposed Changes

• Define bundle abandonment as - there is a pending bundle but after fee increases there are no longer any high enough paying UOs to increase the fees.
• Modify sender state machine to funnel every bundle abandonment to the same state - "replacement underpriced." That is, when a bundle is abandoned clear the transaction tracker and start from scratch. On networks where the previous txn may still be in the mempool, we will get a "replacement underpriced." On other networks, starting from scratch allows us to continue.
• Handle "replacement underpriced" errors with cancellations.
• For the flashbots sender, use a "soft cancellation", which is just an API call and doesn't require polling
• For all other senders, use a "hard cancellation", which requires a transaction to be sent to clear the mempool.

TODO (in follow up PRs):

• Consider splitting the monolith state machine function to make it easier to grok.
• Consider delaying moving to the cancellation state by counting the number of "replacement underpriced" errors without landing a bundle. This will reduce the amount of wasted cancellation funds at the expense of being less reactive.
• Unit testing of bundle_sender