feat: add ActorRefs method to ActorSystem to return the list of actors

[Tochemey]

• ActorRefs method returns a list of active actors, including both local actors and, when cluster mode is enabled, actors across the cluster.
• ActorRef struct to define the information about a given actor:
  • Name: the given actor name
  • Kind: the actor kind
  • Address: the actor address

closes #588

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 4 lines in your changes missing coverage. Please review.

Project coverage is 86.95%. Comparing base (f79eb37) to head (19eda63).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
actors/actor_system.go	75.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #593      +/-   ##
==========================================
+ Coverage   86.72%   86.95%   +0.23%     
==========================================
  Files          56       57       +1     
  Lines        5408     5444      +36     
==========================================
+ Hits         4690     4734      +44     
+ Misses        577      571       -6     
+ Partials      141      139       -2     

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[Tochemey]

QA needed for these changes