feat(rpc): fill size field in getblock with verbosity=2

[conradoplg]

Motivation

This fills the size field in the getblock RPC when verbosity=2.

To support verbosity=1 we would need to either take a performance hit (load all transactions from a block to get their sizes) or change the database to create a tx -> size index (which would be good to avoid if possible)

Might close #9020

Solution

Add a BlockAndSize request to the state which reads the raw block header and txs, gets their sizes, computes the block size from them, and finally parses it all to return the block.

Tests

I adjusted existing tests. I also tested it manually with zcash-rpc-diff.

The block size calculation logic was also tested manually with a throwaway program that computed block sizes from the state with both approaches and asserted that they are equal.

Specifications & References

Follow-up Work

We need to decide if this is enough for now or if we want to support verbosity=1. In that case, we will need to create a new issue for it.

PR Checklist

• The PR name is suitable for the release notes.
• The solution is tested.
• The documentation is up to date.
• The PR has a priority label.
• If the PR shouldn't be in the release notes, it has the
  C-exclude-from-changelog label.

[oxarbitrage]

Looks good to me, thank you.

[oxarbitrage]

thanks @conradoplg

[mergify]

This pull request has been removed from the queue for the following reason: checks failed.

The merge conditions cannot be satisfied due to failing checks:

• ❌ Unit tests / Test integration with lightwalletd
• ☑️ Unit tests / Test CI testnet Docker config file / Test testnet-conf in Docker

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