Test-only driver wrapper that instruments an underlying driver: it
records every operation for later assertion and can inject faults
(connection loss, etc.) to exercise error-handling paths.
Single control handle for the InstrumentedDriver test middleware.
Exposes both the operation log (for assertions) and the fault queue
(for injecting failures). Cheaply cloneable; every clone refers to
the same shared state.
A fault that can be injected into the next operation routed through
the driver. Faults are consumed in FIFO order: each exec call pops
at most one fault off the queue before delegating (or short-circuiting
past) the underlying driver.