Performance refactors

[juanmardefago]

Schema changes:

• Replaced almost all entity IDs with Bytes. Only GraphAccountName still uses ID because of how the id itself was generated.
• Replaced all usages of String to represent entity links with the newly corresponding Bytes
• By replacing ID with Bytes, the IDs themselves have been altered, so they will not match with previous implementations or with the core network subgraph currently (since it still uses String/ID IDs)
• Transaction entities are now immutable
• IndexerDelegatedStakeRelation now only has an ID and a link to the indexer, for performance purposes when handling indexers with lots of delegations

Tests:

• Added a small test to make sure our new Bytes based ID approach works correctly.