Investigate keyCount in MerkleRootChaining test

[jstolarek]

In the offchain/test/Test/MerkleRootChaining.purs test there's a keyCount value. During various recent changes (CTL upgrade, plutus-tx upgrade) we had to lower this value several times to avoid exceeding transaction size limit. The original value was somewhere around 70, now it's 25. Why is this needed? Have the keys themselves grown larger, or have our script sizes increased? Indeed, some of the scripts have increased in size during plutus-tx upgrade, which might account for the increase in the transaction size. Is this an indicator we should be using reference scripts here? We should investigate what exactly is going on.

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IOG Jira: https://input-output.atlassian.net/browse/ETCM-8035