Keep track of transaction information

[Fryuni]

Closes #34

This PR adds support for testing the relation of queries and transactions.

Edit: Transaction stack is managed independently of Knee internal state since it is not exposed.

---

First iteration:

Knex automatically generates a new unique ID for each transaction, passed on the __knexTxId of the connection.

Each nested transaction receives a separate ID, with no relation to its parent. So this PR changes the inline connection object returned by the acquireConnection to a new MockConnection class that keeps track of the transaction stack to properly support nested transactions. Documented here

Sadly, Knex does not revert this ID once a transaction is over as, so far, this is not necessary for any of their driver implementations. As a workaround, we pass the connection down to the tracker, allowing it to walk up the transaction stack when a transaction is completed. Documented here

Also, the transaction ID generated by Knex is globally unique within a process, depending on a global state within one of its dependencies. This makes the ID impractical for tests since they are no predictable. To handle this, the transaction ID from Knex is replaced with a sequential numeric ID that is restarted when resetting the tracker. Documented here

[Fryuni]

Since we have a reference to the connection, we could also not rely on Knex's transaction ID at all.

Your call @felixmosh. I can sent the change if you want.

[Fryuni]

This also solves #32, but only when running inside transactions.

We could have a transaction with ID null representing all the queries that are executed outside of any transactions.

[Fryuni]

The new test should keep track of interleaving transactions is also an example of something that could not be tracked before.

If any of the trx1/trx2 got mixed up, there is no way to detect that till now.

[felixmosh]

@Fryuni I've really this like this approach, and the implementation!
Thank you 🙏🏼

[felixmosh]

Again, thank you for this awesome contribution 🙏🏼

It released at v1.9.0