refac: DRY up New, reuse *All methods, delete modules slice

[abhinav]

The pattern we appear to have for Fx operations (Provide, Invoke, etc.)
take the form:

func (*module) thing(t thing)

func (m *module) thingAll() {
    // perform module-local version of operation
    for _, t := range m.things {
        m.thing(t)
    }

    // recurse into children
    for _, m := range m.modules {
        m.${operation}All()
    }
}

This means that the following two are equivalent:

// 1
for _, m := range app.modules {
    m.thingAll()
}

// 2
app.root.thingAll()

Except (2) is DRYer.

This cleans up New by relying on root-level *All methods
instead of manually iterating over modules.

Making this change also highlighted that 'app.modules'
only ever has one entry: the root module.
So we can delete that field from App as well.

Finally, this also renames:

constructAllCustomLoggers -> installAllEventLoggers
constructCustomLogger     -> installEventLogger
executeInvokes            -> invokeAll
executeInvoke             -> invoke

[abhinav]

This change is part of the following stack:

• refac: DRY up New, reuse *All methods, delete modules slice #1258 ◀

_{Change managed by git-spice.}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.62%. Comparing base (928af08) to head (0ce947f).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1258   +/-   ##
=======================================
  Coverage   98.62%   98.62%           
=======================================
  Files          35       35           
  Lines        3336     3337    +1     
=======================================
+ Hits         3290     3291    +1     
  Misses         39       39           
  Partials        7        7           

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