PolicyEnabler mix-in

[0xJem]

Adds an abstract contract, PolicyEnabler, that can be added to contracts that require the ability to be enabled/disabled. Most policies implement this functionality every time, so this mix-in standardizes the approach and role.

[github-actions]

LCOV of commit 3ec98ae during CI #149

Summary coverage rate:
  lines......: 69.4% (1365 of 1966 lines)
  functions..: 72.2% (296 of 410 functions)
  branches...: no data found

Files changed coverage rate: n/a

[frontier159]

Since this is can be pulled into all policies - I wonder if it'd be worth reducing bytecode by having a toggleIsEnabled() instead of distinct enable and disable functions?

The modifier could be also be a single:

    modifier whenEnabledIs(bool condition) {
        if (isEnabled == condition) revert IsEnabledNotMatching(condition);
        _;
    }

Tradeoff with being explicit - so don't mind, just throwing it out there (MonoCooler is kinda chunky which is why i bring up)

[0xJem]

I feel that the simplicity would be lost, and it also adds ambiguity.

e.g. the whenEnabledIs(bool condition) modifier you shared is reverting if isEnabled == condition, but I would have interpreted it the other way - whenEnabledIs(true) would revert if isEnabled != true

[frontier159]

Totally fair and agree, thought i'd just throw it in the mix.

[frontier159]

LGTM. So the next question is what functions do we add this modifier to on MonoCooler...