Implement constant but relaxation-dependent structure results panel

[edan-bainglass]

This PR implements a structure results panel that is always shown. The tab title and source node are dependent on the nature of the calculation as follows:

• No relaxation - title = "Initial structure"; source = node.inputs.structure
• Some relaxation - title = "Relaxed structure"; source = node.outputs.structure

Auto rendering is adjusted to ensure the initial structure panel is not dependent on having results (there are none) but instead is always auto rendered.

Closes #993

[codecov]

Codecov Report

Attention: Patch coverage is 76.92308% with 6 lines in your changes missing coverage. Please review.

Project coverage is 69.03%. Comparing base (acf4fdb) to head (89ae413).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...qe/app/result/components/viewer/structure/model.py	66.66%	4 Missing ⚠️
...pp/result/components/viewer/structure/structure.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1015      +/-   ##
==========================================
- Coverage   69.19%   69.03%   -0.16%     
==========================================
  Files         117      117              
  Lines        6508     6507       -1     
==========================================
- Hits         4503     4492      -11     
- Misses       2005     2015      +10     

Flag	Coverage Δ
python-3.11	69.03% <76.92%> (-0.16%)	⬇️
python-3.9	69.05% <76.92%> (-0.15%)	⬇️

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[superstar54]

LGTM!