Add per-device options, apply the app's charging minimums with per-device unlock options, add a Delta 2 charge pause switch

[GnoX]

This PR gives the AC charging speed and DC charging current controls the same minimums the EcoFlow app enforces, and adds a per-device advanced option for each so a user who wants to go lower still can. Until now those controls had no lower bound at all on most devices, which is how the 1 W AC charging trick came about: it stops the device drawing from the grid without unplugging it, and it is what solar-surplus automations have been using. The app's floors are per model rather than per family - it dispatches its AC charging range on the serial prefix, giving the Delta 3 and Delta 3 Plus 100 W where the rest of the pd335 family gets 200 W - so each device class declares its own value instead of inheriting one from a base that cannot know which model it ended up on. Because a floor would take the 1 W trick away from Delta 2 owners, this also adds the AC charging pause switch that does the job properly, reading chg_pause_flag (Delta 2) / cfg_pause_flag (Delta 2 Max) and toggling only the trailing pause byte of the AC-charge-set command the speed control already uses.

Full list of changes:

• DeviceOption and DeviceBase.ADVANCED_OPTIONS are the whole mechanism. A device class declares the options it offers, the integration passes the configured values in with with_advanced_options(), and the device reads one back with advanced_option(). Values live under a device_options key in the entry options and are picked up on an options-flow save without a restart.
• option_field() turns a boolean option into a field. Option field reads as either value depending on the option, and declaring it also registers the option in the owner's ADVANCED_OPTIONS, so there is no second declaration to keep in sync.
• Two options rather than one, unlock_ac_charging_minimum and unlock_dc_charging_minimum, so a device only advertises the option for a control it actually has - Delta 2 and Delta Pro 3 offer the AC one alone. Both are unset by default, which means the app's minimum applies.
• AC minimums applied: 200 W across the Delta 2 series and most of the pd335 family, 100 W on the Delta 3 and Delta 3 Plus, 400 W on the Delta Pro 3, 50 W on the River 3 family. The models that subclass a 100 W class without sharing its floor (Delta 3 Max, Max Plus, Ultra) re-declare 200 W, since our class hierarchy nests the larger models under the smaller ones.
• AC charging pause switch for Delta 2 and Delta 2 Max, exposed as an AC Charging switch: on resumes charging, off pauses it, with the watt field of the command left unchanged so the configured speed survives a pause.
• Limit fields renamed to a max/min suffix for consistency with the fields that already read that way. This is a rename of internal fields only - none of them back an entity - and it updates the deprecated number platform's string props and the existing device tests that reference them.

This is a behavior change for anyone already writing a sub-minimum value: an automation that sets 1 W on a Delta 3 or River 3 will now land on the app minimum until the matching option is ticked. Delta 2 owners get the pause switch as the better replacement for that trick.

Resolves #421

[rabits]

Nice change.