Reject negative retry durations

[pragnyanramtha]

Summary

• Reject negative ProfileRetry.duration values during configuration parsing.
• Reuse the same validation for the --retry-duration CLI override.
• Add regression coverage for model parsing and CLI argument handling.

Why

retry.duration represents the maximum retry window. Previously, values like -1 and "-1" parsed successfully, creating nonsensical retry specs instead of a configuration error.

Validation

• uv run pytest src/tests/_internal/core/models/test_profiles.py src/tests/_internal/cli/services/configurators/test_profile.py — 14 passed
• uv run pytest src/tests/_internal/core/models/test_profiles.py src/tests/_internal/core/models/test_runs.py src/tests/_internal/core/models/test_fleets.py — 29 passed
• uv run ruff check . — All checks passed
• uv run ruff format --check src/dstack/_internal/core/models/profiles.py src/dstack/_internal/cli/services/profile.py src/tests/_internal/core/models/test_profiles.py src/tests/_internal/cli/services/configurators/test_profile.py — 4 files already formatted

AI Assistance

This PR was written with AI assistance from OpenAI Codex.

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.