Only load and parse pollfile if it has changed since last loading

[johannaengland]

Scope and purpose

Fixes #282. Dependent on #345.

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• Added a changelog fragment for towncrier
• Added/amended tests for new/changed code
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• Linted/formatted the code with black, ruff and isort, easiest by using pre-commit
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.27%. Comparing base (19ded46) to head (76cdb5b).
Report is 89 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #327      +/-   ##
==========================================
+ Coverage   98.20%   98.27%   +0.07%     
==========================================
  Files          64       64              
  Lines        7930     8029      +99     
==========================================
+ Hits         7787     7890     +103     
+ Misses        143      139       -4     

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[johannaengland]

I have rebased this instead of adding more commit because I have rethought how to access the saved attribute of when the poll file was last modified.

[lunkwill42]

Nice! Still, let me throw some nit-picks at you :)

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[lunkwill42]

Might still consider factoring out the timestamp checking to a separate function, but this will definitely do :)

Runar's suggestion has been fixed.