Allow addNonParallelizableMarkerForTags to mark scenarios non-parallelizable (where supported)

[konarx]

Background
addNonParallelizableMarkerForTags is documented to mark a feature as non-parallelizable. It currently does not apply to scenarios. This makes it difficult to isolate a single scenario without moving it into its own feature or running a separate job. The Reqnroll maintainers have acknowledged that scenario-level parallel isolation isn’t built in.

Proposal (no new config)
Reuse addNonParallelizableMarkerForTags so that when any of its tags appear on a scenario, the generator marks the generated test method as non-parallelizable—but only on frameworks that support scenario-level isolation. Specifically:

1. NUnit: add [NUnit.Framework.NonParallelizable] on the scenario method.
   Docs: https://docs.nunit.org/articles/nunit/writing-tests/attributes/nonparallelizable.html
2. MSTest v2: add [Microsoft.VisualStudio.TestTools.UnitTesting.DoNotParallelize] on the scenario method.
   Docs: https://learn.microsoft.com/en-us/dotnet/core/testing/unit-testing-mstest-writing-tests-attributes#donotparallelizeattribute
3. TUnit: add [TUnit.Framework.NotInParallel] on the scenario method.
   Docs: https://tunit.dev/docs/parallelism/not-in-parallel
4. xUnit: no per-scenario effect (xUnit controls parallelism at collection/fixture level; scenario-level isolation isn’t supported).

The existing behaviour—tagging features to make the whole class non-parallelizable—remains unchanged.

Reasoning

• Many suites have one or two scenarios that touch shared state (e.g., seeding a database), while the rest of the feature can run in parallel.
• Reusing the existing configuration avoids introducing new keys and keeps it intuitive: the same tag marks features or scenarios as exclusive.
• NUnit, MSTest v2, and TUnit support method-level markers; adding per-scenario non-parallelism is straightforward on these frameworks. For xUnit, it’s intentionally a no-op.

Implementation sketch

• When generating each scenario’s method, check if that scenario’s tags intersect with AddNonParallelizableMarkerForTags.
  • If the unit-test provider is NUnit, add [NonParallelizable] to the method.
  • If the provider is MSTest v2, add [DoNotParallelize].
  • If the provider is TUnit, add [NotInParallel].
  • Otherwise (e.g., xUnit), do nothing.
• Leave feature-level logic intact.
• Update docs to clarify that the setting applies to both features and scenarios, with per-scenario effect limited to frameworks supporting scenario-level parallelisation (NUnit, MSTest v2, TUnit).

[konarx]

Opened a draft pull request: #826

[gasparnagy]

This is going to be released with v3.1 soon

[clrudolphi]

Released with v3.1