Disable LTO builds in tests (and bump deps to -O2)

Disable LTO builds in tests (and bump deps to -O2)

For some reason rustc, at some point, decided that our optimization
of dependencies implies we want to also build with LTO. This causes
our test builds to take substantially longer to compile, even with
only a trivial change. By hard-disabling this (even keeping the
optimization of the test and in-tree libraries enabled) the time
required to build with only a trivial change to
`functional_tests.rs` goes from 0m25.635s wall clock/1m14.220s CPU
time to 0m17.841s wall clock/0m17.828s CPU time on my i7-13700K on
rustc 1.63.

The changes in test execution time appear to be within noise.

While we're at it, we also bump dependencies to build with -O2
because their build time is now substantially reduced cost.