Vault rounding and complementary debt functions

[0xdcota]

This pull request addresses multiple vulnerabilities and issues reported in the Macro report audit.

M-2 Vault rounding inconsistencies L-6 Lack of option of fully payback loan Q-2 Unnecessary use of _msgSender() Q-3 Double conversion of assets<>shares in withdraw function flow G-1 and G2 Immutable definition of vault asset and debtAsset

[0xdcota]

@pedrovalido updated all the missing docs in TODOs. This should be ready to be merged.

[pedrovalido]

Great! Let's merge then