* Do not call `import socket` on each send()/recv() when using rustls
Use method references cached during socket creation.
* Implement reading of at most one TLS record from socket
Previous algorithm didn't take into account that recv() may return less
data than requested even for blocking sockets.
* Remove special handling of rustls "buffer full" errors
First of all, existing code does not really work and this leads to an
infinite loop: https://github.com/RustPython/RustPython/issues/7891
Second, this should never happen when rustls used properly (wrt
wants_read() and wants_write()) and thus all such errors are
implementation bugs that must be properly fixed.
* Replace own TlsConnection with rustls::Connection
* Fix waiting on a socket
1) Ensure that socket_wait() called from TLS glue code allows threads
2) Ensure that socket_wait() called from TLS glue code properly handles
EINTR on *nix
3) Ensure that select() or poll() error conditions are checked
4) Use poll() on *nix so socket descriptor values are not limited
* Remove dead code from rustls glue
* Do not present rustls errors as OSError(0, "Success")
* Remove infinite loop "detection" from rustls glue
TLS handshake cannot be infinite. Any infinite loop here is a serious
bug in implementation and should be fixed properly.
This code triggers in some cases (very short reads) with misleading
`ssl_error.SSLWantReadError: The operation did not complete (read)`.
* Add test for 1-byte max recv in TLS client
* Add regression test for https://github.com/RustPython/RustPython/issues/7891
* Fix constants in rustls glue code
* Deduplicate verify flags / record-size constants
* Larger "max encrypted TLS record length"
