statedb: Fix read-after-write bug

[joamaki]

statedb: Fix read-after-write bug

The optimization in *txn to hold the last used index read transaction
to avoid a hash map lookup was broken as the write txn used for reading
was cloned, leading to not being able to read any of the future writes
in the same transaction.

  txn := db.WriteTxn(table)
  table.Insert(txn, Foo{ID: 1})
  table.First(txn, IDIndex.Query(1)) // works as it caches the clone of just created indexWriteTxn
  table.Insert(txn, Foo{ID: 2})
  table.First(txn, IDIndex.Query(2)) // fails as the cloned transaction doesn't see the insert

Benchmark show that this optimization does not actually help, so solve
the problem by removing the optimization.

Before:
BenchmarkDB_RandomLookup-8 1000000 1471 ns/op

After:
BenchmarkDB_RandomLookup-8 1000000 1485 ns/op

Fixes: d0d4d46 ("statedb: Store index unique info in the index tree entry")

Note that v1.14 does not have the "StateDB v2.0", so it is not affected by this.

Fix a bug in the StateDB library that may have caused stale read after write. This may have potentially affected the L2 announcements feature and the node address selection.

[joamaki]

/test

[joamaki]

/test