fix: support the php-code-coverage 14.3 line coverage shape

[maks-oleksyuk]

php-code-coverage 14.3 changed the shape of ProcessedCodeCoverageData::lineCoverage(). A line used to hold the list of test ids covering it; it now holds hit counts keyed by an index into a separate list returned by testIds().

Mutation testing reads that structure to work out which tests cover a mutation. Against 14.3 it receives integers where strings are expected, and every run aborts on the first covered mutation with preg_match(): Argument #2 ($subject) must be of type string, int given.

phpunit/phpunit allows phpunit/php-code-coverage: ^14.2.3, so both shapes are in circulation and both have to keep working.

What changed

MutationTestRunner::coveredLines() normalises the coverage data into [file => [line => [testId, ...]]] before anything consumes it. testIdsCoveringLine() tells the two shapes apart by their structure rather than by a version check: a string value is a test id from 14.2 and earlier, an integer key is an index into the ids reported by 14.3.

This also clears the two pre-existing PHPStan errors on MutationTestRunner, which were the same mismatch surfacing statically.

Testing

tests/Unit/Tester/MutationTestRunnerTest.php covers both shapes, an index with no matching test id, and a line nothing covers.

Follow-ups

Mutation sharding builds on this fix in #40 and #41, and on pestphp/pest#1829.

[devfake]

would be great to have this merged. the error is preg_match(): Argument #2 ($subject) must be of type string, int given. current fix is to downgrade to phpunit/php-code-coverage:14.2.4.