Prestwich/gas escalator dangle

[prestwich]

Fixes #2269

Motivation

Task spawn was causing dangling tasks when GasEscalator dropped, as no messaging notified the task to close

Solution

GasEscalatorMiddleware is split into 3 things:

• GasEscalatorMiddleware: a simple wrapper around an arc for safe cloning
• GasEscalatorMiddlewareInternal: Holds the inner mware, the shutdown channel, and a ref to the tx vec
• EscalatorTask: the running escalation task. Periodically attempts to escalate the transactions

What I fixed:

• dangling tasks
• a very long mutex guard hold
• gas escalator now always cheaply cloneable
• remove clone bounds from some functions

What I didn't fix:

• if the escalation task crashes, the mware will still become unusable, but not inform you of this or error. This is not a change from previous behavior, however, it sucks. It would require a much larger fix tho

What this introduces

• if the user drops all middleware, escalation will cease. this seems like good, expected behavior

PR Checklist

• Added Tests
• Added Documentation
• Updated the changelog
• Breaking changes

[gakonst]

One idea I had is that maybe we pull SignerMiddleware to ethers-signers and we otherwise pull out ethers-middleware to a separate repo, as these are starting to be a maintenance overhead and are not part of the "core" evolving suite.

[prestwich]

One idea I had is that maybe we pull SignerMiddleware to ethers-signers and we otherwise pull out ethers-middleware to a separate repo, as these are starting to be a maintenance overhead and are not part of the "core" evolving suite.

i'd like to address this in ethers-next

also, don't merge master into branches :P