kip-227: fill CandTesting at epoch start blocks

[ian0371]

Proposed changes

Fill CandTesting to header.VRank at epoch start blocks

Types of changes

• Bugfix
• KIP Proposal
• KIP Improvement

Checklist

• Used the suggested template: https://github.com/kaiachain/KIPs/blob/main/kip-template.md
• I have read the CLA and signed by comment I have read the CLA Document and I hereby sign the CLA in first time contribution
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

Related issues

#27

Further comments

[hyunsooda]

Currently the usage of VRank looks scattered throuight the specification. To clarify, how do you think to add "VRank encodes different payloads depending on block position" with the two category: non-epoch and epoch

For example,

┌───────────────────────┬─────────────────────────────────────────────┐
│    Block position     │                header.VRank                 │
├───────────────────────┼─────────────────────────────────────────────┤
│ N % EPOCH_LENGTH != 0 │ RLPEncode(cfReport(N)), or nil if empty     │
├───────────────────────┼─────────────────────────────────────────────┤
│ N % EPOCH_LENGTH == 0 │ RLPEncode(CandTesting(N)) (MUST NOT be nil) │
└───────────────────────┴─────────────────────────────────────────────┘

[ian0371]

@hyunsooda updated. PTAL