Rework the event based handling of transfers and connections to
be "localized" into a single source file with clearer dependencies.
- add multi_ev.c and multi_ev.h
- add docs/internal/MULTI-EV.md to explain the overall workings
- only do event handling book keeping when the socket callback
is set
- add handling for "connection only" event tracking, when internal
easy handles are used that are not really tied to a connection.
Used in connection pool.
- remove transfer member "last_poll" and connections "shutdown_poll"
and keep all that internal to multi_ev.c
- add CURL_TRC_M() for tracing of "multi" related things, including
event handling and connection pool operations. Add new trace
feature "multi" for trace config.
multi traces will show exactly what is going on in regard to
event handling.
- multi: trace transfers "mstate" in every CURL_TRC_M() call
- make internal trace buffer 2048 bytes and end the silliness
with +n here -m there. Adjust test 1652 expectations of resulting
length and input edge cases.
- add trace feature "lib-ids" to perfix libcurl traces with transfer
and connection ids. Useful for debugging libcurl applications.
Closes#16308
- delete completed TODO from `./CMakeLists.txt`.
- convert a C++ comment to C89 in `./CMake/CurlTests.c`.
- delete duplicate EOLs from EOF.
- add missing EOL at EOF.
- delete whitespace at EOL (except from expected test results).
- convert tabs to spaces.
- convert CRLF EOLs to LF in GHA yaml.
- text casing fixes in `./CMakeLists.txt`.
- fix a codespell typo in `packages/OS400/initscript.sh`.
Closes#11772
