Feat/vesting contract

[JoE11-y]

This Pr Resolves #53

Work Done

1. Added Vesting Contract that supports both Cliff and Linear vesting types
2. Added Tests

[JoE11-y]

@raduciobanu22 this is ready for review

[raduciobanu22]

@JoE11-y A few notes after checking the PR:

• I would have preferred to rely on a more straightforward approach to calculate claimable amount using only start, duration, current block and amount claimed so far. Using predefined milestones makes the contract less flexible. A good blueprint is the OpenZeppelin VestingWallet contract and also the VestingWalletCliff contract that extends it.
• In general, smart contract code has to be very efficient, which means relying on math tricks vs loops. Something to keep in mind
• Support for fungible tokens is required besides ALPH
• Cliff support is required

Thanks for the effort!

[JoE11-y]

Hi @raduciobanu22 thanks for taking the time to review the PR and share your thoughts. I appreciate the feedback! I just wanted to clarify a few things and share my perspective:

1. Cliff Support: Cliff is already supported, as shown in the tests. It’s also designed to work seamlessly with linear vesting when setting milestones, giving flexibility to combine both approaches if needed.

2. Predefined Milestones: The idea behind using predefined milestones was to give creators more control to design vesting schedules exactly how they want. I thought this would make the contract more adaptable to different needs.

3. Multiple User Vesting: One of the key benefits of this implementation is that it supports multiple users in a single contract, which simplifies things and avoids the need for deploying separate contracts for each user.

4. Loops: I get the concern around loops, but in this case, the loop’s impact is minimal once the nextMilestone variable is kept up-to-date.

[JoE11-y]

@raduciobanu22 made the changes as requested.

[raduciobanu22]

@raduciobanu22 made the changes as requested.

I think the only thing missing is support for fungible tokens..
Btw, there's a built-in function for the ALPH amount that needs to be deposited when creating a sub-contract: https://docs.alephium.org/ralph/built-in-functions/#minimalcontractdeposit

Thanks for the refactoring, looking good!

[JoE11-y]

Done with it @raduciobanu22