## Why this should be merged
Registration of extras requires runtime enforcement of payload types. In
production, only a single set of types can be registered and any
attempts at re-registration will panic (by design). Although this makes
production usage safe, it doesn't allow downstream consumers (e.g. data
indexers) to use extras from different chains (e.g. `coreth` _and_
`subnet-evm`) at the same time.
## How this works
1. The `libevm/register.AtMostOnce` type can now be overridden
temporarily.
2. `params`, `core/types`, `core/vm`, and `state` packages introduce
`WithTempRegisteredExtras()` functions.
3. `libevm/temporary.WithRegisteredExtras()` provides "atomic" override
of all extras.
In all cases, the scope of the override is limited to the life of a
single function call.
## How this was tested
Relative to numbered list above:
1. Unit test of new and existing functionality.
2. Integration tests of both packages, demonstrating both payload and
behavioural override.
## Why this should be merged
`ava-labs/coreth` has a partitioned state-address space, achieved by
setting or clearing a specific bit in the hash used to key the space.
This change allows such behaviour to be achieved with pure `libevm`
instead of the `StateDB` wrapping that `coreth` currently uses.
## How this works
Introduction of `state.StateDBHooks` interface, including a
`TransformStateKey()` method that allows for arbitrary change of state
key. If registered, this hook will be honoured by
`StateDB.{Get,GetCommitted,State}Key()` methods unless they receive a
`stateconf.SkipStateKeyTransformation` option.
## How this was tested
Unit test of `SetState() -> GetState() + GetCommittedState()` round trip
with and without options to skip.
## Why this should be merged
Coreth and Subnet-EVM require access to the current tx hash in the Warp
precompile (for selecting the correct predicate results).
This can not be exposed as a wrapper through the `OverrideEVMResetArgs`
because `SetTxContext` is called _prior_ to resetting the EVM instance.
Therefore, the `SetTxContext` function on any DB wrapper would never be
called.
## How this works
Exposes the existing `txHash` through a `TxHash()` function.
## How this was tested
Added a trivial unit test.
## Why this should be merged
Allows for a drop-in replacement of `snapshot.Tree` (i.e. one that uses
block hashes instead of state roots). This is intended as a temporary
solution while we investigate having the state root affected by the
block hash to remove path ambiguity.
## How this works
Introduction of:
1. `state.SnapshotTree` interface to match methods required on
`snapshot.Tree` as used by `state.StateDB`; and
2. `stateconf` package for variadic options plumbed by
`StateDB.Commit()` through to `SnapshotTree.Update()`.
Although variadic (to maintain function call-signature compatibility)
only the `stateconf.WithUpdatePayload(any)` is expected to be used.
Recipients of the options can access the payload with
`stateconf.ExtractUpdatePayload()`.
## How this was tested
Unit test demonstrating propagation of `stateconf.UpdateOption` payload.
