Drop support for `calls.pkl` and fix an issue with multiprocessing

[cuihantao]

See release notes.

[codecov[bot]]

Codecov Report

Merging #362 (dc93327) into develop (cd0f10e) will increase coverage by 0.10%. The diff coverage is 88.23%.

@@             Coverage Diff             @@
##           develop     #362      +/-   ##
===========================================
+ Coverage    78.36%   78.46%   +0.10%     
===========================================
  Files          178      178              
  Lines        14655    14614      -41     
===========================================
- Hits         11484    11467      -17     
+ Misses        3171     3147      -24     

Impacted Files	Coverage Δ
andes/utils/paths.py	81.48% <ø> (-1.13%)	:arrow_down:
andes/system.py	80.00% <86.66%> (+1.55%)	:arrow_up:
andes/main.py	63.24% <100.00%> (ø)

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[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication