feat: full solver failure surcharge solution

[BenSparksCode]

Changes to Accounting Treatment of Surcharges

Variables

• cost = the base gas cost of execution, on which surcharges are calculated.
• a = Atlas gas surcharge
• b = Bundler surcharge
• d = deficit due to insufficient solver balance during _assign()

Latest Accounting Rules

• When a solver wins:
  • No change in rules. Surcharges are calculated on the full metacall gas cost.
  • Bundler receives cost + b, paid by winning solver.
  • Atlas receives a, paid by winning solver.
• When zero solverOps:
  • No surcharges applied.
  • Bundler incurs cost and does not receive a refund.
  • Atlas does not receive any surcharge.
• When some solverOps, but all fail:
  • claims is set to 0, but the following treatment is applied on a per-solverOp basis.
  • When solverOp failure is the Bundler's fault:
    • Solver pays nothing.
    • Bundler incurs cost, and writeoffs increases by a + b, but gets cleared when claims gets set to 0 unless their is a winning solver.
    • Atlas does not receive any surcharge.
  • When solverOp failure is the Solver's fault:
    • Solver pays cost + a + b - d via _assign().
    • Bundler incurs cost but is refunded cost + b - d via _credit().
    • Atlas receives a via an increase in cumulative surcharge.

Capping Bundler refund when all solverOps fail

• Introduced in feat: cap bundler surcharge if all solvers fail #441

Bundling should not be profitable when all solvers fail. If they fail due to fault of the solver, the current accounting charges Atlas and Bundler surcharges on the gas costs of the execution of those SolverOperations. This was then distributed to Atlas and Bundler at the end of the metacall.

However, the Bundler may also collect storage refunds after bundling a metacall, which in combination with the Bundler surcharges, could result in a profitable tx (ETH spent on gas cost vs refunds and surcharges received). As such, we now cap the Bundler surcharge, only in the case of all solvers failing, to a max of 80% of the metacall gas cost. The remaining 20% may be made up through storage refunds.

If the max is exceeded, the excess is instead taken as Atlas gas surcharge.

[jj1980a]

lgtm!