[Execution State] Reduce encoded payload value length from 8 bytes to 4 bytes in checkpoint file

[fxamacker]

Problem

Currently, the entire payload length is encoded to 4 bytes while the payload value length is encoded to 8 bytes. So reducing to 4 bytes makes sense.

This encoding is used in checkpoint, TrieUpdate (WAL), and TrieProof. Since this affects code outside checkpoint, it was moved from PR #1944 to this separate issue.

Thanks @ramtinms and @tarakby for confirming we should reduce this length.

Updates epic #1744

The Proposed Solution

Use 4 bytes to encode payload value length instead of 8 bytes.

Caveats

Estimate is 3 (limited scope) or 7 (larger scope) depending on the approach taken to resolve this.

[fxamacker]

This was closed by PR #2165 on March 17, 2022.