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>

docs/SPORTS_UNIFICATION.md

@@ -80,11 +80,30 @@ src/base_classes/sports/
 src/common/
   sports_scroll.py       SportsScrollDisplay / …Manager — scroll orchestration
                          (content building stays in the plugins)
+  sports_helpers.py      clamp/logo/rotation free functions + SportsHelpersMixin
+                         (unreleased) — the helpers byte-identical in the
+                         plugins' sports.py, and the _favorite_key seam
 ```
 
 `from src.base_classes.sports import SportsCore` keeps working — the package
 `__init__` re-exports, so the conversion is invisible to every existing importer.
 
+### Converging on `src/common`
+
+The scoreboards do not build on `src/base_classes`; their own `sports.py` copies
+have moved past it. So shared code now lands in hardware-free `src/common`
+modules taken from the plugin copies, each a **new module** rather than growth
+on an existing one: a plugin that deletes a method copy and relies on an older
+module having gained it fails at runtime with an `AttributeError`, while a
+missing module fails at load, where the version checks can see it.
+`sports_helpers.py` is the first (it holds `_favorite_key`, the override point
+listed below, for later phases); its parity test compares every body against
+the plugin copies when `LEDMATRIX_PLUGINS` points at a checkout, and
+`test/test_common_is_hardware_free.py` keeps `src/common` free of
+`rgbmatrix`, `src.base_classes` and `src.plugin_system`. How a plugin adopts a
+module and drops its copy is documented in the plugins repo's
+`docs/plugin-development/08-shared-sports-code.md`.
+
 ## Override points (the plugin-facing seam)
 
 The base class calls these; plugins implement or override them. This table is the