7.0.0

CHANGES:

• adapt to TLS 1.0.0 API changes, bump OCaml lower bound to 4.13 (#432 @hannesm)
• conduit-lwt-unix: improve the no TLS error message (#431 @filipeom)
• Remove 4.12 CI runners, add 5.2 (#433 @art-w)
• Update GitHub actions (#429 @smorimoto)
• use failwith instead of Lwt.fail_with, use Lwt.reraise (#430 @MisterDA)
• switch to sexplib0 instead of sexplib for lighter dependencies (#427 @emillon)