v2.6.1-beta.10

Fix: issue #159 - cost statistics crash and options persistence

Fixes

• Removed unit_class='monetary' from cost statistic metadata — HA 2026.2 rejects it as unsupported. Cost statistics now omit unit_class entirely.
• Added missing @callback decorator to async_get_options_flow — this may fix options not persisting after Submit.
• 72 tests passing