Revert "feat!: read code coverage config from Cypress.expose instead of Cypress.env"

[cacieprins]

Reverts #972

The commit message needs to be updated in order to trigger semantic-release

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Note

Medium Risk
Changes the public configuration mechanism back to env, which can break users relying on the newer expose behavior, and also modifies CI/runtime versions (Node/Cypress base images) that may surface environment-specific failures.

Overview
Reverts the plugin’s configuration surface from Cypress.expose back to Cypress.env/env.codeCoverage (docs, example configs like cypress-backend.json, and middleware usage comments updated accordingly).

Migrates several TypeScript helper/middleware modules to CommonJS JavaScript (common-utils.js, middleware/*) and removes the old TS entrypoints (lib/*), while adding a Cypress project (cypress.config.js, cypress/ e2e specs) to test option combining, spec/support filtering, and coverage merging/placeholder handling.

Updates CircleCI to restructure test execution: adds a dedicated plugin test job, runs example test-apps via a matrix job, downgrades Cypress Docker base images/Orb version, and adjusts the Windows job to Node 20.

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