Respond with latest for pending block number requests

[BedrockSquirrel]

Why this change is needed

Some tools are making RPC requests to us with 'pending' blocknumber which was erroring.

These are the eth block number options:

They don't map that well to obscuro batches. For now this treats those requests the same as for latest block because it's better than failing, and I will create an issue for us to revisit this.

We may eventually want to respond with the latest batch that's been rolled up for the 'finalized' flag but maybe that's not intuitive behaviour when rollups may take hours.

What changes were made as part of this PR

Handle the nuanced cases of eth block number all as 'latest' batch for now, in particular pending which wasn't supported.

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Commits

Files that changed from the base of the PR and between 563c567 and 064c0e0.

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