- A method that has `?` suffix should return boolean, but this method return an object that respond to `valid?`.
- All other examples don't have `?`.

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Explain clean vs compare in README

…/checkout-4

Bump actions/checkout from 3 to 4

Fix example code in README

Fix bug with marshalling experiments

CI against Ruby v3.3

We'd like to be able to quantify CPU time consumed while executing
the candidate and control blocks during science experiments.

Changes include:
- Added `cpu_time` attribute to `Scientist::Observation`.
- Refactored initialization to capture both start/end times for wall
time and CPU time.
- Updated tests to include CPU-intensive work so we can verify we're
recording CPU time correctly.

This allows us to track cpu time more precisely when making improvements.

This supports both the old version (single value) and new version (hash-based).

I've added back the tests from the old version to check that the code stills works
when we provide a single value.

I've also adapted the README a bit to explain both versions.

Report CPU Time alongside Wall Time