Add child operations from supervision tree AND type_id support

[slawlor]

This patch does 2 things

1. Adds ability to access the type id and runtime check the message type of an ActorCell. RE: Query the type_id of an actor at runtime #276
2. Adds ability to stop & drain children actors, by traversing the supervision tree, instead of requiring users to hold the handles themselves in the states. RE: post_stop of children are being called when supervisor fails. #226

[codecov]

Codecov Report

Attention: Patch coverage is 90.06623% with 30 lines in your changes missing coverage. Please review.

Project coverage is 80.47%. Comparing base (defec7f) to head (a230487).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
ractor/src/actor/tests/supervisor.rs	93.10%	12 Missing ⚠️
ractor/src/actor/actor_cell.rs	79.48%	8 Missing ⚠️
ractor/src/actor/supervision.rs	88.23%	8 Missing ⚠️
ractor/src/actor/tests/mod.rs	86.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #277      +/-   ##
==========================================
+ Coverage   80.20%   80.47%   +0.26%     
==========================================
  Files          60       60              
  Lines       10671    10972     +301     
==========================================
+ Hits         8559     8830     +271     
- Misses       2112     2142      +30     

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