[*.py] Use f-strings and os.path.join throughout

[SamuelMarks]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 87.17949% with 15 lines in your changes missing coverage. Please review.

Project coverage is 85.05%. Comparing base (ad7bbb8) to head (70fa3ea).

Files with missing lines	Patch %	Lines
keras/src/applications/efficientnet_v2.py	70.00%	3 Missing ⚠️
keras/src/applications/inception_v3.py	0.00%	2 Missing ⚠️
keras/src/datasets/cifar100.py	0.00%	2 Missing ⚠️
keras/src/utils/file_utils.py	75.00%	2 Missing ⚠️
keras/src/applications/mobilenet_v3.py	80.00%	1 Missing ⚠️
keras/src/callbacks/model_checkpoint.py	0.00%	1 Missing ⚠️
keras/src/saving/file_editor.py	80.00%	1 Missing ⚠️
keras/src/utils/model_visualization.py	0.00%	1 Missing ⚠️
keras/src/utils/progbar.py	75.00%	1 Missing ⚠️
keras/src/utils/summary_utils.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21343      +/-   ##
==========================================
+ Coverage   82.68%   85.05%   +2.36%     
==========================================
  Files         565      565              
  Lines       54829    54838       +9     
  Branches     8513     8513              
==========================================
+ Hits        45335    46640    +1305     
+ Misses       7409     5998    -1411     
- Partials     2085     2200     +115     

Flag	Coverage Δ
keras	84.86% <87.17%> (+2.37%)	⬆️
keras-jax	66.02% <85.47%> (+2.38%)	⬆️
keras-numpy	58.89% <38.46%> (+0.11%)	⬆️
keras-openvino	33.26% <17.94%> (+0.13%)	⬆️
keras-tensorflow	66.41% <86.32%> (+2.39%)	⬆️
keras-torch	66.03% <84.61%> (+2.37%)	⬆️
keras.applications	83.60% <91.30%> (?)
keras.applications-jax	83.60% <91.30%> (?)
keras.applications-numpy	22.81% <5.79%> (?)
keras.applications-openvino	22.81% <5.79%> (?)
keras.applications-tensorflow	83.60% <91.30%> (?)
keras.applications-torch	83.33% <91.30%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.