Nothing checks the four copies of the version agree

[Chemaclass]

Problem

The version lives in four places, and release.sh bumps all four together:

file	carrier
bashunit	BASHUNIT_VERSION="0.47.0"
action.yml	default: '0.47.0'
install.sh	LATEST_BASHUNIT_VERSION="0.47.0"
package.json	"version": "0.47.0"

release_update_test.sh covers those updaters against mock files, which
proves the functions work — not that the repo's own four copies currently
agree. They can drift from a release that failed partway, a hand-edit, or a
merge resolved the wrong way.

Each drift fails differently and quietly:

• action.yml stale → every TypedDevs/bashunit@v0 user installs an old binary
• install.sh stale → the documented curl-installer pins the wrong release
• package.json stale → npm publishes under a version that is not this code

None of it surfaces in a test run.

Fix

Assert the four agree, reading the entrypoint as the source of truth.

Includes a guard on the guard: if the version extraction ever stops matching,
every assertion would compare "" against "" and pass while checking
nothing — so one test asserts the extracted value is a real version string.

Mutation-verified: desyncing each of the three dependents fails exactly its own
test.

[Chemaclass]

Done in #1193 (merged).