Cleanup Epoch and EpochStake schemas' entities

[manumonti]

GraphQL schema changes:

• Epoch counter's unique entity ID Singleton have been replaced by epoch-counter to have a more meaningful name.
• EpochStake entities only contains the fields staking provider address and amount. participation and stakeData fields have been removed to avoid redundant data.
• The timestamp field name of an epoch have been replaced by timestamp. The total amount of token staked in a epoch entity is saved in totalAmount field (previously totalStaked).
• Now, the first epoch (number 0) is the period between the token staking contract deployment and the first staking event.
• Comments format have been homogenized.

Src files changes:

• Added src/utils/epochs.ts code with some utilities related to the management of the epochs and its counter.
• Modified HandleStaked function in mapping.ts to follow the new schema (handleToppedUp and handleUnstaked are pending).
• Unstaked handle function adapted to new schema
• ToppedUp handle function adapted to new schema

[cygnusv]

There were already some format changes in a recent commit (see https://github.com/threshold-network/subgraph/commit/525e470b04a8f71670fa6a29df5f687c8934a203). This PR shouldn't try to reintroduce the old format, unless that's agreed with @r-czajkowski. Ideally, this should be part of a linter pre-commit strategy, rather than changes within PRs, which make review more difficult and noisy

[manumonti]

There were already some format changes in a recent commit (see 525e470). This PR shouldn't try to reintroduce the old format, unless that's agreed with @r-czajkowski. Ideally, this should be part of a linter pre-commit strategy, rather than changes within PRs, which make review more difficult and noisy

Done!

[manumonti]

I don't want to be a blocker here so approving this PR. I left my concerns here and maybe we should consider removing the stakes from Epoch entity(ofc if at all possible) and find EpochStakes between dates by query in a script that will l generate a merkle tree.

I'm not sure if I'm understanding well, or if it's better in terms of performace to have the EpochStakes saved in subgraph or to calculate them with a script. But we can discuss this in other PR if you're ok with it.