EthTxHashLookup has poor query management

[rvagg]

Noticed in a heap dump:

EthTxHashLookup#UpsertHash creates a new PreparedStatement on each call and then does nothing else with it (probably should be closed at a minimum). The remainder of the queries don't use PreparedStatements at all.

TODO:

• Refactor to use PreparedStatements for all queries not involved in migration
• Retain PreparedStatement instances on the parent EthTxHashLookup for re-use

Should be done after #12098 is merged, or done on top of that branch.

[jennijuju]

Can also be a good issue for Mikers