state: build_diff() reports deletions for accounts that never existed

[chfast]

#1709 fixed one instance of this: an account warmed up by a cold access and then reverted was reported in StateDiff::deleted_accounts. The artifact still appears when the account is inserted some other way and ends up empty.

The shortest case is a transaction to an address that does not exist — state_transition.tx_legacy, where 0xc0de is not in the pre-state:

tx.to = To;  // no code, no value

execute_message() inserts the recipient with erase_if_empty, it ends empty, and build_diff() puts it in deleted_accounts. Same for a non-existent SELFDESTRUCT beneficiary (state_transition.touch_nonexistent_sd, 0x4e).

build_diff() skips m.nonexistent (set only when a revert restores the account) and m.just_created (set only by CREATE). There is no flag for "inserted because it was touched", so these fall through to the erase_if_empty branch.

As with #1709 the state is correct — applying such a delete is a no-op — so only the diff is affected.

Scale: adding this to the state_transition fixture fails 28 of 132 tests on master:

for (const auto& a : receipt.state_diff.deleted_accounts)
    EXPECT_TRUE(pre.contains(a)) << a << ": deleted, never existed";

Related, and already noted in the TODO below: modified_accounts also lists accounts that were only read or warmed, with nonce and balance unchanged — e.g. state_transition.touch_access_list_storage_only, where 0x5a is warmed by the access list alone.

#1717 adds an in_diff expectation to the state_transition fixture, which can be used to pin down whatever behaviour is decided here.