feat(pytest-plugin): negative assertion methods

[bepri]

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assert_messages and assert_interactions are out of scope as they are different search mechanisms that don't really need negation available.

Closes #489

[Copilot]

🟡 Changes recommended

The assertion API is incomplete and inconsistently named, required Ruff suppressions need restoration, and negative-regex coverage is missing.

2 open findings

• Retain PLC0415 suppression for Windows-only import · New
• Retain PLC0415 suppression for test-local import · New

What changed in this PR

Adds negative assertion helpers to the pytest recording emitter and tests their behavior.

Changes:

• Adds assert_no_* helpers with regex and progress support.
• Adds tests for negative assertions.
• Updates Ruff lint suppressions for local imports.

File	Summary
tests/​test_pytest_plugin.py	Tests negative assertion behavior.
tests/​integration/​test_messages_integration.py	Updates import lint suppressions.
craft_cli/​pytest_plugin.py	Implements negative assertion helpers.
craft_cli/​messages.py	Updates Windows-only import lint handling.

🧠 Review effort: Lite

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[Copilot]

🟡 Changes recommended

Unresolved API coverage, lint failure, and missing test coverage remain.

2 open findings

• Wrap error message to satisfy the 88-character line limit · New
• Add negative forms for multi-message and interaction assertions · New

2 resolved since last review

• Retain PLC0415 suppression for test-local import
• Retain PLC0415 suppression for Windows-only import

🧠 Review effort: Lite