The three switch-coordination rules

Example module: hellotypes, switchoneofmany/switchatmostone/switchany properties.

Several ElementBool elements within the same property can be coordinated with each other like radio buttons or independent checkboxes, via "rule" in the property’s JSON:

`rule`	Behavior
`0` — `OneOfMany`	Exactly one true at a time (radio). Setting an element to `true` resets all the others to `false`. Setting it back to `false` directly is refused — another one must be chosen instead.
`1` — `AtMostOne`	Zero or one true (optional radio). Same behavior, except it can also be directly deselected.
`2` — `Any` (default)	No constraint, independent checkboxes.

"switchoneofmany": {
  "permission": 2,
  "rule": 0,
  "e": {
    "calibrate": { "type": "bool", "directedit": true },
    "guide":     { "type": "bool", "directedit": true },
    "stop":      { "type": "bool", "directedit": true }
  }
}

Fully declarative: the actual enforcement of the rule lives in the framework itself, triggered by any write to one of the elements — no code to write in the module for it to work, only to set a consistent initial state if needed.