This updates to the 2027-1 toolchains. This also is the first version
with the `rules_bzlmodrio_toolchains -> wpilib_toolchains` rename, so
the surface area of the change is a little bit big.
The opencv dep has bzlmod'ified as part of this as well.
There were complaints about no patch files being created from CI when
the examples pre-gen fails for people who don't build with bazel. This
adds a new action step to run just the non-robotpy pregen.
I also added an argument to the diff tests to make it a unified diff,
which might make it easier to hand fix.
