fix(frontends/lean/calc_proof_elaborator): improve calc proof assistant
refactor(library/data/nat/basic): remove unnecessary `{}`
refactor(library/algebra/category/basic): use calc assistant
feat(frontends/lean/calc_proof_elaborator): add 'elaborator.calc_assistant' option
feat(frontends/lean/calc_proof_elaborator): when 'elaborator.calc_assistant' is on, generate same info that is generated if `!` was used