feat(common): sports_helpers — the helpers all nine scoreboards carry identical copies of (#583)

* feat(common): sports_helpers, the helpers all nine scoreboards copy verbatim

Add src/common/sports_helpers.py: the helpers the scoreboard plugins'
sports.py carry byte-identical copies of (docstring-stripped AST, checked at
ledmatrix-plugins f09bff2), so a later plugins PR can delete its copies once
it floors on the core release that ships this.

- Free functions: clamp_window, clamp_seconds, logo_needs_refresh (lazy
  src.logo_downloader import, as in the plugins), spread_weighted_order,
  MIN_WINDOW_DAYS / MAX_WINDOW_DAYS. All nine plugins.
- SportsHelpersMixin (no __init__, stateless): _mode_customization,
  _setting_int, _reset_dwell_on_reentry, _next_switch_index,
  _spread_weighted_order (all nine), _odds_color and
  _upcoming_date_and_time_text (all but ufc), plus the _favorite_key seam
  from base_classes core.py for later phases.

A new module rather than more methods on sports_shared: a plugin that
deletes a copy and relies on an existing module having grown the method
fails at runtime with AttributeError on an older core, which neither the
loader nor check_min_core_version.py can see; a missing module fails at load.

Tests: behaviour for every helper, a derived host contract, and a parity
test that AST-compares every body against every plugin copy when
LEDMATRIX_PLUGINS points at a checkout (skipped otherwise).
test_common_is_hardware_free.py imports src.common and every sports_* module
with rgbmatrix blocked and scans src/common for module-level imports of
src.base_classes, src.display_manager and src.plugin_system (no existing
violations).

Nothing in core imports the new module; no behaviour change. CHANGELOG
Unreleased entry and a converging note in docs/SPORTS_UNIFICATION.md.
__version__ is not bumped.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* fix(common): address review on sports_helpers and the hardware-free test

- SportsHelpersMixin docstring and CHANGELOG: constructor-free, but it keeps
  lazy state on its host (_reset_dwell_on_reentry, _next_switch_index).
- test_common_is_hardware_free: the runtime check now filters every
  FORBIDDEN package, src.plugin_system included; the AST scan resolves
  relative imports against src.common, so `from .. import plugin_system`
  and `from ..plugin_system import x` are caught. Guard tests for both.
- Parity skip reason names the CI guard that runs the same comparison:
  ledmatrix-plugins scripts/check_sports_helpers_parity.py (#495).
- _odds_color: line-level pylint disable for a not-callable false positive
  (getter is None-checked); the AST is unchanged, parity still passes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -19,6 +19,26 @@ accepts both, but the store flags the old spelling as deprecated
 
 ## Unreleased
 
+New module a plugin may import via `src.*` (floor on the release that ships
+this):
+
+- `src/common/sports_helpers.py` — the helpers the scoreboards' `sports.py`
+  carry byte-identical copies of: `clamp_window`, `clamp_seconds`,
+  `logo_needs_refresh`, `spread_weighted_order` (+ `MIN_WINDOW_DAYS`,
+  `MAX_WINDOW_DAYS`), and `SportsHelpersMixin` with `_mode_customization`,
+  `_setting_int`, `_reset_dwell_on_reentry`, `_next_switch_index`,
+  `_spread_weighted_order`, `_odds_color`, `_upcoming_date_and_time_text` under
+  the plugins' names and signatures, plus the `_favorite_key` override point.
+  Constructor-free; keeps lazy state on its host (see the module docstring,
+  which also gives the host contract).
+  A new module rather than more methods on `sports_shared`: a plugin that
+  deletes a copy and leans on an older module having grown the method fails at
+  runtime with `AttributeError`, which no load-time check sees, while a missing
+  module fails at load. Nothing in core uses it yet.
+- `test/test_common_is_hardware_free.py` — `src/common` must import without
+  `rgbmatrix` and never import `src.base_classes`, `src.display_manager` or
+  `src.plugin_system` at module level.
+
 ## 3.4.0
 
 Plugin-facing changes since 3.3.0 (tag `v3.3.1`) not covered further down: