EVM-607 Hard-forking PoC

[igorcrevar]

Description

Forking Manager PoC

Example:
Let's say we have three forks: A, B, and C, with starting blocks 0, 10, and 20, respectively. For each fork, we have a simple handler that returns a string. We can achieve this using the code example below

fm := GetInstance()

const handlerDesc = "fn"

type handlerFn func() string

// define handlers
var (
    h1 handlerFn = func() string { return "Handler for fork A" }
    h2 handlerFn = func() string { return "Handler for fork B" }
    h3 handlerFn = func() string { return "Handler for fork C" }
)

// register forks
fm.RegisterFork("A")
fm.RegisterFork("B")
fm.RegisterFork("C")

// register handlers
assert.NoError(t, fm.RegisterHandler("A", handlerDesc, h1))
assert.NoError(t, fm.RegisterHandler("B", handlerDesc, h2))
assert.NoError(t, fm.RegisterHandler("C", handlerDesc, h3))

// activate forks
assert.NoError(t, fm.ActivateFork("A", 0))
assert.NoError(t, fm.ActivateFork("B", 10))
assert.NoError(t, fm.ActivateFork("C", 20))

// check if appropriate handler is called for some block number
for i := 0; i < 50; i++ {
    handler := fm.GetHandler(handlerDesc, uint64(i)).(handlerFn)
    
    if i < 10 {
	 assert.Equal(t, "Handler for fork A", handler())
    } else if i < 20 {
	 assert.Equal(t, "Handler for fork B", handler())
    } else {
	 assert.Equal(t, "Handler for fork C", handler())
    }
}

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Breaking changes

Please complete this section if any breaking changes have been made, otherwise delete it

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

Manual tests

Please complete this section if you ran manual tests for this functionality, otherwise delete it

Documentation update

Please link the documentation update PR in this section if it's present, otherwise delete it

Additional comments

Please post additional comments in this section if you have them, otherwise delete it

[vcastellm]

Can you add a small code example on how a handler should be used?

[vcastellm]

Can you add a small code example on how a handler should be used in the PR body?

[igorcrevar]

Example is here #1567

[goran-ethernal]

[vcastellm]

LGTM