Implement Finalizable in GrandpaService

[Grigorov-Georgi]

Description

• Polkadot Spec: https://spec.polkadot.network/sect-finality#algo-finalizable & https://spec.polkadot.network/sect-finality#defn-grandpa-completable
• Calculating Grandpa Ghost seems expensive operation and to reduce overhead, I've updated certain methods to accept a precomputed Ghost as a parameter, so we can reuse it. For flexibility, if Ghost is null, the method will compute it on the spot.
• The current implementation doesn't align fully with the spec and refactoring is required. Currently we are assuming that all of the prevotes/percommits in the state are from the current round. Refactoring on isCompatible and isFinalizable will be provided in the next PR.

Fixes #398

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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