Reduce clutter in restart dict

[alongd]

Don't save default values of ARC, ARCSpecies, and ARCReaction objects as dictionaries
Tests modified accordingly

[codecov]

Codecov Report

Attention: Patch coverage is 54.45545% with 46 lines in your changes missing coverage. Please review.

Project coverage is 73.67%. Comparing base (34ef50d) to head (728aeea).

Files	Patch %	Lines
arc/main.py	25.71%	11 Missing and 15 partials ⚠️
arc/species/species.py	67.27%	8 Missing and 10 partials ⚠️
arc/reaction.py	66.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #751      +/-   ##
==========================================
- Coverage   73.77%   73.67%   -0.11%     
==========================================
  Files          99       99              
  Lines       27364    27406      +42     
  Branches     5723     5765      +42     
==========================================
+ Hits        20189    20190       +1     
- Misses       5748     5768      +20     
- Partials     1427     1448      +21     

Flag	Coverage Δ
unittests	73.67% <54.45%> (-0.11%)	⬇️

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[JintaoWu98]

LGTM!