Update makedocs syntax and few cleanups

[sathvikbhagavan]

1. Updated makedocs syntax for Documenter@1
2. Formatted the repo
3. Dropped 1.6 in CI as the compat in Project.toml for julia is 1.9

[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (71a6206) 65.20% compared to head (a9c4fa0) 78.12%.
Report is 1 commits behind head on master.

Files	Patch %	Lines
src/Sampling.jl	50.00%	3 Missing ⚠️
src/Optimization.jl	33.33%	2 Missing ⚠️
src/Radials.jl	0.00%	2 Missing ⚠️
src/VirtualStrategy.jl	33.33%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #452       +/-   ##
===========================================
+ Coverage   65.20%   78.12%   +12.91%     
===========================================
  Files          23       23               
  Lines        3144     3154       +10     
===========================================
+ Hits         2050     2464      +414     
+ Misses       1094      690      -404     

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