chore: release date for m5

doc: add slide headers to examples

chore: remove some `partial`

refactor: address review comments

chore: disable check in the prelude `inferInstance` helper functions

refactor: introduce a few double-backtick quotations

feat: release 4.0.0-m2

chore: fix test

chore: fix LEAN_SPECIAL_VERSION_DESC

feat: delaborator: use implicit lambdas where possible

/cc @leodemoura it's not bullet-proof (unless `pp.explicit` is set), but let's
see if it is good enough in practice