Implement transaction layer that stores all changes in memory

Nobody has claimed this yet.

We can implement transaction layer similar to described here: https://neo4j.com/docs/cypher-manual/current/introduction/transactions/

The idea is to store all transitions from source link state to target link state. So if we receive any of source link state we should substitute it with target state in `Each` (read) function. If any of link conflicts with the transition, changing source data or applying different target state at the same location then we should immediately fail the transaction.

After all changes are ready to be applied we acquire write lock, do recheck of all conflicts, if everything is fine we write all changes in a single batch. At the end write lock is released.

Start by reviewing the existing Each read function and the code paths that change source link data, then map how link states and conflicts are currently represented. The transaction layer is done when changes remain in memory, conflicting transitions fail immediately, final conflicts are rechecked under a write lock, and valid changes are written in one batch.

Written by the indexing model from the issue text.