Feat: coverage in shards

[MrPunyapal]

What:

• Bug Fix
• New Feature

Description:

This PR adds first-class coverage support for sharded Pest runs and fixes the CI/composer setup required to run that flow reliably.

It solves two concrete problems:

• --coverage and --shard=X/Y did not provide a built-in way to collect coverage from each shard and merge it into one final report.
• CI dependency resolution could be inconsistent in detached HEAD environments when resolving the root package together with dev dependencies such as pestphp/pest-plugin-browser.

What changed:

• pest --shard=X/Y --coverage now stores coverage as .cov files under .pest/coverage/ instead of trying to render a report per shard.
• pest --shards-coverage now merges all shard coverage files and prints one combined coverage report.
• --shards-coverage supports the existing coverage thresholds via --min and --exactly, supports --only-covered, and can clean up temporary coverage files with --clean.
• During sharded coverage runs, output-style coverage report flags are stripped and Pest shows a follow-up command to run after all shards finish.
• Help output and coverage tests were updated to document and verify the new flow.
• CI now sets COMPOSER_ROOT_VERSION=4.x-dev and uses the supported Symfony floors (7.4.8 and 8.0.8) so dependency resolution stays stable across the matrix.

How To Use Locally:

Run each shard with coverage enabled:

pest --shard=1/2 --coverage
pest --shard=2/2 --coverage

Merge the generated shard coverage files into one final report:

pest --shards-coverage

Useful local variants:

pest --shard=1/3 --coverage
pest --shard=2/3 --coverage
pest --shard=3/3 --coverage

pest --shards-coverage --min=80
pest --shards-coverage --exactly=91.5
pest --shards-coverage --only-covered
pest --shards-coverage --clean

Notes:

• Shard coverage files are written to .pest/coverage/{shard}.cov.
• --clean removes the temporary .cov files after the merged report is generated.
• If a sharded run receives output-oriented coverage flags, Pest warns and points you to the merge step instead.

How To Use In CI:

1. Run each shard in a parallel job and upload .pest/coverage/ as an artifact.
2. In a follow-up job, download all shard artifacts then run the merge.

# shard jobs (run in parallel, e.g. strategy matrix)
- run: php bin/pest --shard=${{ matrix.shard }}/3 --coverage
- uses: actions/upload-artifact@v4
  with:
    name: coverage-shard-${{ matrix.shard }}
    path: .pest/coverage/

# merge job (depends on all shard jobs)
- uses: actions/download-artifact@v4
  with:
    pattern: coverage-shard-*
    merge-multiple: true
    path: .pest/coverage/
- run: pest --shards-coverage --min=80 --clean

20260424-1834-59.9415647.mp4