feat: adding channel subscription method and tests

[germa89]

Description

Adding a method to retrieve the gRPC channel status through channel subscription.

Issue linked

NA

Checklist

• I have visited and read Develop PyMAPDL.
• I have tested my changes locally
• I have added necessary documentation or updated existing documentation.
• I have followed the PyMAPDL coding style guidelines.
• I have added appropriate unit tests that also ensure the minimal coverage criteria.
• I have reviewed my changes before submitting this pull request.
• I have linked the issue or issues that are solved to the PR if any.
• I have assigned this PR to myself.
• I have marked this PR as draft if it is not ready to be reviewed yet.
• I have made sure that the title of my PR follows Commit naming conventions (e.g. feat: adding new MAPDL command)

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[germa89]

Reference: https://grpc.github.io/grpc/core/md_doc_connectivity-semantics-and-api.html

GRPC Core: gRPC Connectivity Semantics and API

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 6 lines in your changes missing coverage. Please review.

Project coverage is 87.12%. Comparing base (a8b1514) to head (a51a318).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3340      +/-   ##
==========================================
- Coverage   87.13%   87.12%   -0.02%     
==========================================
  Files          55       55              
  Lines        9773     9810      +37     
==========================================
+ Hits         8516     8547      +31     
- Misses       1257     1263       +6     

[germa89]

@pyansys-ci-bot LGTM.

[pyansys-ci-bot]

✅ Approving this PR because germa89 said so in here 😬