Tokenized vaults example

[iFrostizz]

https://eips.ethereum.org/EIPS/eip-4626

tldr; A vault that can be used as a token that is indexed on an asset that is the underlying token.
The exchange rate is always tracked and holds some properties that could be left tested more thoroughly as part of a future work:
Let define the exchange rate (R) as assets (A) / shares (S)

• Deposit of assets:
  • S' >= S
  • A' >= A
  • R' >= R
• Withdrawal of assets:
  • S' <= S
  • A' <= A
  • R' <= R
• Corectness of rounding:
  • The pool is always advantaged (rounds towards the pool) and user is disadvantaged. This ensures that the pool cannot be emptied by a repeated deposit / withdraw

The token needs to be built prior to running tests because otherwise it will complain that the wasm binary cannot be found. Two hacks here (we probably want to create some kind of packaging system with dependency resolution):

• The token binary path is figured by taking the vault binary path
• The token is compiled by manually changing the env variable names inside of the build script and putting it back to build the vault afterwards