Feature/improve log loading

[hrntsm]

Reference Issues/PRs

What does this implement/fix? Explain your changes.

• Improve result log file load speed.
  • Tunny was loading the result file when launching the UI, and when the log file was large, it took a long time to launch.
  • With this update, log files are now about 60 times faster to load.
    • What used to take about 5 minutes to load the results of 30,000 trials can now be loaded in about 5 seconds.

[codeclimate]

Code Climate has analyzed commit 9a27c3f and detected 12 issues on this pull request.

Here's the issue category breakdown:

Category	Count
Complexity	3
Duplication	9

View more on Code Climate.

[codecov]

Codecov Report

Attention: Patch coverage is 53.30882% with 127 lines in your changes missing coverage. Please review.

Project coverage is 45.06%. Comparing base (9334e6f) to head (9a27c3f).
Report is 5 commits behind head on develop.

Files with missing lines	Patch %	Lines
Optuna/Storage/Journal/Storage.cs	53.30%	110 Missing and 17 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #424      +/-   ##
===========================================
- Coverage    45.57%   45.06%   -0.52%     
===========================================
  Files           67       67              
  Lines         3030     3180     +150     
  Branches       332      365      +33     
===========================================
+ Hits          1381     1433      +52     
- Misses        1610     1700      +90     
- Partials        39       47       +8     

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