Change pg_session_connection_failed to include a failure reason

[SeanTAllen]

Adapts postgres internals to three breaking lori releases between 0.8.1 and 0.11.0:

• 0.9.0: _on_connection_failure() and _on_tls_failure() now take a reason parameter
• 0.11.0: expect() takes (Expect | None) instead of USize

The lori failure reasons are now threaded through the state machine to the public API: pg_session_connection_failed on SessionStatusNotify takes a ConnectionFailureReason — a closed union of ConnectionFailedDNS, ConnectionFailedTCP, SSLServerRefused, TLSAuthFailed, and TLSHandshakeFailed.

Other mechanical changes: FFI declarations in _mort.pony updated to match lori's, a mock server test fixed (moved send() from constructor to _on_started()), and MakeExpect(1) matches made exhaustive with _Unreachable().

Closes #161

[ponylang-main]

Hi @SeanTAllen,

The changelog - changed label was added to this pull request; all PRs with a changelog label need to have release notes included as part of the PR. If you haven't added release notes already, please do.

Release notes are added by creating a uniquely named file in the .release-notes directory. We suggest you call the file 163.md to match the number of this pull request.

The basic format of the release notes (using markdown) should be:

## Title

End user description of changes, why it's important,
problems it solves etc.

If a breaking change, make sure to include 1 or more
examples what code would look like prior to this change
and how to update it to work after this change.

Thanks.