feat!: Make Timer and TimerComponent APIs consistent

[ufrshubham]

Description

Makes the Timer and TimerComponent APIs consistent.

Previously TimerComponent took a named period, while Timer took a positional limit. Also, TimerComponent exposed a public onTick method that wrapped the user callback, which could go out of sync with Timer.onTick.

Changes:

• Timer now takes a required named period (was positional limit), and the Timer.limit field is renamed to Timer.period.
• TimerComponent.onTick() is removed. The callback passed to the constructor is set directly on the internal timer, and tickWhenLoaded calls timer.onTick.
• Updated SpawnComponent, HasBehaviorTree, docs, examples and tests accordingly.

Checklist

• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change.
• No, this PR is not a breaking change.

Migration instructions

If the PR is breaking, uncomment this header and add instructions for how to migrate from the
currently released version in-between the two following tags:

Before:

final timer = Timer(1, repeat: true, onTick: tick);
timer.limit = 2;

class MyTimer extends TimerComponent {
  MyTimer() : super(period: 1, repeat: true);

  @override
  void onTick() => tick();
}

After:

final timer = Timer(period: 1, repeat: true, onTick: tick);
timer.period = 2;

class MyTimer extends TimerComponent {
  MyTimer() : super(period: 1, repeat: true) {
    timer.onTick = tick;
  }
}

Related Issues

Closes #2386

[spydon]

Lgtm, why did we build it that inconsistent to begin with... 😆