Metrics verification

[Alexey-Ostrovsky]

CHANGES:

• C4 & C5 registers depth: Mostly just terminology correction. In relation to the account state (C4 register), there is no difference. However, the actions register has its own serialization format: a list of cell references, which ends with a cell containing only an end tag. This means that the number of actions, limited by this parameter, is 512 - 1 = 511. Nevertheless, the actual limit is the "hardcoded" max_action parameter, which currently has a value of 255. I added a separate string for it. In practice, this means that if the number of actions is between 255 and 511, an error will occur during the action phase, not the compute phase. Perhaps we should consider omitting C5 to avoid confusing the reader.
• Also fixed the description for (mc_)delete_due_limit.

NOTES:

• block_gas_limit: Despite its presence in the global config and as an in-code value, I didn't find any payload connected to this parameter. It seems that this parameter is just being copied/packed/serialized all around, but doesn't have any effect on transaction behavior. Nevertheless, I didn't risk deleting it and would prefer to get a comment from one of the TON maintainers.

[Alexey-Ostrovsky]

Created PR to documentation for clarification of those moments:

ton-community/ton-docs#882