[mlir-lsp] Un-revert unit test additions (#90232)

This reverts the revert commit 6844c2fe, which was comprised
of the following commits:

1. f3f6f22d - [mlir-lsp] Initialize `Reply::method` member (#89857)
2. 37e13d49 - [mlir-lsp] Log invalid notification params (#89856)
3. ba1b52e6 - [mlir-lsp] Add `outgoingNotification` unit test
4. 84bc21f9 - [mlir-lsp] Add transport unit tests (#89855)

Of these, (4) specifically caused issues in Windows pre-merge buildbots,
in the `TransportTest.MethodNotFound` unit test that it added. The
failure was caused by a statement that asserted that opening a file
stream on a newly created temporary file did not result in an error, but
this assert failed on Windows.

This patch adds additional error logging for failures, to make it
clearer what went wrong when failures occur. This patch also addresses
the Windows failure by ensuring temporary files are created in the
system temporary directory.