feat: native pytest-bdd support

[gibiw]

Summary

• Adds automatic Gherkin step capture for pytest-bdd scenarios in qase-pytest — no manual qase.step() instrumentation required
• Preserves Given/When/Then semantics, scenario hierarchy, DataTable/DocString contents, Scenario Outline parameters
• Tag-based metadata on scenarios: @qase.id=, @qase.suite=, @qase.severity=, @qase.priority=, @qase.layer=, @qase.ignore, @qase.muted, @qase.project_id.CODE=
• Nested qase.step() inside a step function attaches as a child of the Gherkin step (parent_id hierarchy)
• Zero changes to qase-python-commons; pytest-bdd>=7.0,<9.0 is a testing extra, not a runtime dependency

Architecture

• New module qase.pytest.bdd (QasePytestBddPlugin) registered conditionally in conftest.py only when pytest_bdd is importable
• Bridges six pytest-bdd hooks (before/after_scenario, before/after_step, step_error, step_func_lookup_error) to existing Runtime.add_step() / finish_step() and Result field mutations
• Pure helpers: parse_scenario_tags, format_data_table, format_docstring, build_step, enrich_result_from_scenario

Test plan

• Unit tests for tag parser, data-table / docstring formatters, step builder, result enrichment (56 tests in test_bdd_helpers.py)
• Plugin unit tests with mocked hooks (test_bdd_plugin.py — covers all 6 hooks including happy path, failure path, lookup error, skipped tail, ignore flag)
• Pytester-based integration tests (10 scenarios: basic, failing tail, lookup error, nested qase.step(), scenario outline, DataTable + DocString, tags, ignore, coexistence with plain pytest)
• Manual run of examples/single/pytest-bdd/ against local report driver — JSON output verified end-to-end
• Full qase-pytest suite: 100 passed
• Manual run against a real Qase TestOps project — pending before merge

Known limitations / follow-ups

• The local report driver in qase-python-commons flattens StepGherkinData into StepTextData (action="<Keyword> <name>", input_data=table/docstring). TestOps API mode preserves native Gherkin structure; this only affects JSON-report inspection. Worth a separate PR in commons if rich JSON Gherkin shape is desired.
• pytest-bdd 8.x packs Scenario Outline parameters as a single _pytest_bdd_example argument with a serialized dict. Individual columns (a, b, c) are not split — works correctly but the parameter name is opaque. Possible enhancement: parse and re-expose as separate Qase params.

Customer reproduction

examples/single/pytest-bdd/ reproduces the customer scenario from the original feature request — login.feature with 3 Gherkin steps, each containing a nested qase.step(). Run pytest -v from that directory and inspect build/qase-report/results/*.json to see the full hierarchy.