protocol upgrade (v2): Burn slashed rewards (phase RD 1) + changes to system epoch info event

[oliviasaa]

Description of change

• Changes in the reward distribution so the slashed rewards from a validator are not redistributed to the others.
  Phase RD 1: In this phase, the grading and reporting of validators remain unchanged. Instead of adjusting rewards so that slashed rewards are assigned to non-slashed validators, we remove this adjustment, entirely burning the slashed rewards, which would go to the protocol instead of going to the non-slashed validator set.
• Change the information about burned tokens amount in the SystemEpochInfoEventV1 (emitted from the advance_epoch function)

Links to any relevant issues

Fixes #3123

Type of change

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• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How the change has been tested

The reward amounts were tested and checked for both slashed and non-slashed validators

Change checklist

Tick the boxes that are relevant to your changes, and delete any items that are not.

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked that new and existing unit tests pass locally with my changes

[valeriyr]

LGTM!

[lzpap]

LGTM!

[kodemartin]

lgtm