Postfix with smtpd_forbid_bare_newline (default hardening since 3.9,
after SMTP smuggling) rejects the message with
"521 5.5.2 Error: bare <LF> received". RFC 5321 requires CRLF.
The python sender is unaffected (smtplib already emits CRLF).
fix https://github.com/acmesh-official/acme.sh/issues/7104
Add and use _readaccountconf_mutable_default and
_saveaccountconf_mutable_default helpers to capture
common default value handling.
New approach also eliminates need for separate
underscore-prefixed version of each conf var.