docs: enhance documentation with NatSpec for all public functions

[zerosnacks]

Related: foundry-rs/book#1303

To do:

• Interfaces chore: unify interface NatSpec #666
• Base.sol
• console.sol
• console2.sol
• safeconsole.sol
• Script.sol
• StdAssertions.sol
• StdChains.sol docs: add NatSpec @notice to public functions #860
• StdCheats.sol docs: add NatSpec @notice to public functions #860
• StdError.sol
• StdInvariant.sol
• StdJson.sol docs: add NatSpec @notice to public functions #860
• StdMath.sol
• StdStorage.sol docs: add NatSpec @notice to public functions #860
• StdStyle.sol docs: add NatSpec @notice to public functions #860
• StdToml.sol docs: add NatSpec @notice to public functions #860
• StdUtils.sol
• Test.sol
• Vm.sol

Goals:

• Document all public facing functions with @notice
• Mark private variables and functions with underscore prefix refactor: prefix private members with underscore #861
• Unify layouts to follow common best practices of grouping storage variables
• Move internal functions up, private functions down
• Should not modify any user facing function or interface

This will make it easier to autogenerate documentation that we can then load into https://book.getfoundry.sh/reference/forge-std/ and keep it up to date

[Ra9huvansh]

Hi, I'd like to work on StdAssertions.sol and StdInvariant.sol for this, adding NatSpec to public functions, reordering by visibility, and underscore-prefixing private vars. Will submit a PR soon.