Store already added node viewer and load it when needed

[superstar54]

Reopen PR #560 .
In aiidalab-widgets-base/viewer.py, it creates a new viewer every time we select a new AiiDA node, and the viewer is not saved in the app, so we can not reuse it later. This has two drawbacks:

• The performance is back. user needs to wait every time when selecting a new node.
• One can not call the viewer later, e.g., for reset.

This PR stores the already added viewer and reuses it later.

This is also needed in the lazy-loading PR.

[codecov]

Codecov Report

Attention: Patch coverage is 28.57143% with 10 lines in your changes missing coverage. Please review.

Project coverage is 66.92%. Comparing base (2924582) to head (3de6ff9).
Report is 127 commits behind head on main.

Files with missing lines	Patch %	Lines
src/aiidalab_qe/app/result/__init__.py	28.57%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #921      +/-   ##
==========================================
- Coverage   67.06%   66.92%   -0.14%     
==========================================
  Files          51       51              
  Lines        4715     4726      +11     
==========================================
+ Hits         3162     3163       +1     
- Misses       1553     1563      +10     

Flag	Coverage Δ
python-3.11	66.92% <28.57%> (-0.14%)	⬇️
python-3.9	66.95% <28.57%> (-0.14%)	⬇️

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[edan-bainglass]

@superstar54 thank you for reopening this! It will greatly improve the usefulness of the lazy-loading work implemented in #802 w.r.t the results section. Will review ASAP!

[edan-bainglass]

LGTM! As stated, this will come in handy when node_views become MVCs. Good to not have to recreate them 🙂