Wrapped MultiNode client

[dhaidashenko]

Wrapped over MultiNode and lazy-loaded client to ensure components like LogPoller can interact with them without need to handle error returned on RPC selection.
See comment.

[reductionista]

Isn't this redundant with the prior initialization?

ch.multiClient = client.NewMultiClient(ch.getClient)

Either way, if the multinode is enabled the same SelectRPC() function will be called, right?

// getClient returns a client, randomly selecting one from available and valid nodes
// If multinode is enabled, it will return a client using the multinode selection instead.
func (c *chain) getClient() (client.ReaderWriter, error) {
	if c.cfg.MultiNode.Enabled() {
		return c.multiNode.SelectRPC()
	}

[reductionista]

Actually I just re-read @DylanTinianov's comment on my PR and saw he's proposing to get rid of the MultiNode path from c.getClient. If we do that, then I think this makes sense as-is.

[reductionista]

We could either do that in this PR, or in my PR

[dhaidashenko]

Removed second initialization of multiClient.
We can't remove the MultiNode path from c.getClient as it's by other methods of the chain struct.

[cl-sonarqube-production]

Quality Gate failed

Failed conditions
4.5% Coverage on New Code (required ≥ 75%)

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