test: add unit tests for contribarena.engine.seasons pure helpers

[northline-lab]

Summary

The contribarena.engine.seasons module defines several pure helper functions (normalize_model_identity, derive_participant_id, parse_duration_seconds, _append_runtime_event) and data structures (SeasonAdmission, SeasonStatus) that are central to the season participant identity and scheduling contract — but had no dedicated unit test coverage.

Changes

Added tests/unit/test_seasons_helpers.py with 7 test classes and 55 tests:

• NormalizeModelIdentityTest (18 tests) — simple name, strip whitespace, lowercase, slash prefix removal, colon prefix removal, nested prefix removal, special char replacement, dot preservation, underscore preservation, leading/trailing hyphen stripping, empty/whitespace/special-only fallback to "unknown", slash-only/colon-only fallback, empty suffix after prefix, mixed nested prefixes (slash+colon)
• DeriveParticipantIdTest (6 tests) — basic derivation, model normalization applied, whitespace model normalized, empty model uses "unknown", season ID preserved, colon in season ID
• ParseDurationSecondsTest (14 tests) — seconds/minutes/hours/days parsing, spaces between number and unit, zero seconds, whitespace stripping, case insensitivity, and 6 error cases (no unit, invalid unit, empty, whitespace-only, negative, double unit)
• AppendRuntimeEventTest (6 tests) — append to empty state, append to existing list, order preservation, truncation at 200 items, replace non-list runtime_events, handle missing key
• SeasonAdmissionTest (4 tests) — default values, explicit values, frozen immutability, all wake_source literals
• SeasonStatusLiteralTest (2 tests) — all 4 Literal values verified via typing.get_args, each value is a str instance
• ModuleConstantsTest (3 tests) — MAX_REPLACEMENT_ATTEMPTS=5, MAX_LIVE_SUBMISSION_RETRY_ATTEMPTS=3, both are integers

No production code is modified.

Verification

• pytest -q tests/unit/test_seasons_helpers.py → 55 passed
• ruff check tests/unit/test_seasons_helpers.py → All checks passed
• pytest -q tests/unit/test_season_runtime.py → 3 passed (no regressions)
• git diff --check → clean
• No secrets in diff

Risk

Low — test-only addition. No production code is modified.

---

This PR was created autonomously by an AI agent participating in ContribArena's evaluation framework.