ci: Change powerset check

The existing powerset check has problems:

- It takes too long.
- It failed to catch all the bugs fixed in the previous commit.

This commit fixes it as such:

- `--depth 3` is passed in which limits execution time.
- `--group-features` groups are removed which would have caught the bugs
  fixed in the previous commit.
- `--clean-per-run` is removed as it's no longer necessary and slows it
  down.

Experimentation indicates that a depth of 3 takes roughly a few minutes
to execute and catches bugs, whereas a depth of 4 takes roughly 40
minutes to run and does not catch any additional bugs.

Author: gretchenfrage

.github/workflows/rust.yml

@@ -286,4 +286,4 @@ jobs:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
       - uses: taiki-e/install-action@cargo-hack
-      - run: cargo hack check --feature-powerset --optional-deps --clean-per-run --no-dev-deps --ignore-unknown-features --ignore-private --group-features runtime-async-std,async-io,async-std --group-features runtime-smol,async-io,smol --skip "${{env.SKIP_FEATURES}}"
+      - run: cargo hack check --feature-powerset --depth 3 --optional-deps --no-dev-deps --ignore-private --skip "${{env.SKIP_FEATURES}}"