* fix(http): join multipart request bodies with CRLF
Multipart parts are delimited by CRLF per RFC 2046; prepare() joined
body lines with LF, so strict servers (Tomcat) never found the boundary
and rejected the request as 413. Join with CRLF when the request's
Content-Type is multipart/*; other bodies keep LF.
Fixes#1700
* ci: retrigger after flaky mybatis test on windows
* ci: retrigger after flaky java debug smoke