Add optional extra delay before first target of condition

[lkeegan]

• add pre_first_target_extra_delay key to Trial
  • time is added to pre_first_target_delay for the first target of a set of conditions
  • default value: 0
• update docs
• resolves #235

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov[bot]]

Codecov Report

Merging #236 (da6bee5) into main (b1348da) will increase coverage by 0.03%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #236      +/-   ##
==========================================
+ Coverage   89.32%   89.36%   +0.03%     
==========================================
  Files          19       19              
  Lines        1499     1504       +5     
==========================================
+ Hits         1339     1344       +5     
  Misses        160      160              

Impacted Files	Coverage Δ
src/vstt/trial.py	73.58% <ø> (ø)
src/vstt/task.py	92.91% <100.00%> (+0.11%)	:arrow_up:
src/vstt/vtypes.py	98.61% <100.00%> (+0.01%)	:arrow_up: