Increased gas efficiency in Beefy vaults smart contracts

[0xdanielvigo]

This PR focuses on improving gas efficiency across the vaults smart contracts by applying several optimization techniques, including:

• Setting variables to constant or immutable when applicable.
• Replacing revert strings with custom errors.
• Using unchecked in calculations that will not underflow / overflow.

These changes aim to reduce overall gas usage while maintaining readability and functionality.

[0xdanielvigo]

Added custom reverts and unchecked blocks since they are more gas efficient also when setting the optimizer to true or when using --via-ir.

In withdraw functions such as BeefyVaultV7::withdraw() i directly assigned _after to r, because it avoids unnecessary calculations and thus saves gas.
NOTE: r = b + (_after - b) is the same thing as doing r = _after.