Add support for execution sharding

[agologan]

🤔 What's changed?

• Adds new flag --shard 1/3 to allow for execution sharding similar to https://playwright.dev/docs/test-sharding

⚡️ What's your motivation?

Tackles #2303

🏷️ What kind of change is this?

• 📖 Documentation (improvements without changing code)
• ⚡ New feature (non-breaking change which adds new behaviour)

♻️ Anything particular you want feedback on?

Feature is implemented as plugin on event pickles:filter and will run between filter and order plugins.
As such defined order is not affected by sharding and random order will only shuffle tests in a shard.

Alternatively, a new event pickles:shard could be introduced to be executed after pickles:order which would allow a global random seed. This will require a documentation change to warn users they should use the same seed across shards.

The option was added to ISourcesCoordinates as it acts more like a filtering option for a specific instance rather than how --parallel behaves and the plugin was loaded only for runCucumber.

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

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[coveralls]

coverage: 97.79% (+0.01%) from 97.78%
when pulling 64169d3 on agologan:main
into aac018c on cucumber:main.