fix(tia): record new dependencies of known tests on coverage runs

[lazerg]

What:

• Bug Fix
• New Feature

Description:

On --tia --coverage runs, Graph::replaceEdges() is called with keepExisting: true and skips every test file that already has edges. A test that starts using a new file never gets that edge, so a later change to the file replays the test as passed.

This takes the change suggested in the issue: with keepExisting, the new edges are added to the recorded set instead of being dropped. The coverage report still cannot narrow a recorded set, and a plain --tia run still replaces it.

The new test in tests/Features/Tia/CoveragePiggyback.php makes Greeter call Calculator and expects app/Calculator.php in the edges of GreeterTest after a coverage run. It fails on 5.x in the sequential and parallel datasets. It skips without a coverage driver, like the xml coverage test above it.

Related:

Fixes #1953