Use `bash` in all the CI `test.sh` scripts, for no particular reason
other than to be uniform with other scripts in the repository.

Instead of running the linter in each individual CI script we can just
run it once from the top level script and exit. This has the benefit of
being quicker with no loss of linting coverage. Note this does remove
sanity builds from the linting job, this does not reduce overall
coverage of the whole CI workflow.

As we did for the linting stuff, move the docs stuff out of each
individual CI script and into the top level script. Reducing code
duplication with no reduction in test coverage.

These MSRV pinning blocks are stale, remove them.

The CI script is overly complex to reason about because of how it
interacts with the github actions. In an effort to make it more obvious
exactly what is going on and what is failing when CI is red split the
linting and docs stuff out into separate jobs. In the CI script once
these are run exit. This has the added advantage of making these jobs
fast to run and fast to fail, hopefully making the dev feedback loop
quicker.

We do not run the formatter in CI anymore, remove the stale logic from
all test scripts.

As we did for linting and docs; move the bench stuff to the top level
script and run it in a separate job.

These variables are no longer used, remove them.

The `AS_DEPENDENCY` test does not need to be run for the recent and
minimal lock files, just run it once in a separate job.

The ASAN tests do not use `cargo --locked` so can be run from the top
level CI script.

This patch _increases_ coverage because the job that enables DO_ASAN was
only being run in `hashes/` - now we run it in `fuzz/` as well.

Note please I'm not very knowledgeable about ASAN stuff or what exactly
is going on in these commands but I remove `--lib` (and added `+nightly`
to be explicit) in order to get the it working in `fuzz/`.

The WASM test does not use `cargo --locked` so we can run it from the
top level CI script.

The individual CI scripts are expected to be run after copying the
recent/minimal lock files into place. As such all `cargo` commands
should be run with `--locked` otherwise the lockfile will be updated. To
save us making mistakes in the future introduce a variable `CARGO` and
always use it instead of `cargo`.

This patch changes the current behaviour because in some places the
sanity checks are being run without using `--locked` - this is a bug.

The current CI github action uses the name 'Continuous integration'
which is really long and noisy - use CI with no loss of clarity.

TIL, one can use curly braces and only redirect a single time - thanks
`shellcheck`.

Refactor only, no logic changes.

`shellcheck` complains about unused `FEATURES` variable, leave it there
commented out to make explicit the non-uniformity of this script
compared to the others. I'd say there is some work left to do to clean
up the feature matrix stuff.