feat: Allow passing sleep to commands

[tony]

addressed by #750

Blocked by #751

#748

commands:

session_name: 'sleep command'
windows:
- panes:
    - shell_command: echo "___$((1 + 3))___"
      sleep: 3

[codecov]

Codecov Report

Merging #749 (fef242a) into master (091cb56) will increase coverage by 0.12%.
The diff coverage is 100.00%.

❗ Current head fef242a differs from pull request most recent head 93b4ff1. Consider uploading reports for the commit 93b4ff1 to get more accurate results

@@            Coverage Diff             @@
##           master     #749      +/-   ##
==========================================
+ Coverage   76.05%   76.17%   +0.12%     
==========================================
  Files           7        7              
  Lines        1186     1192       +6     
  Branches      312      313       +1     
==========================================
+ Hits          902      908       +6     
  Misses        197      197              
  Partials       87       87              

Impacted Files	Coverage Δ
tmuxp/workspacebuilder.py	85.78% <100.00%> (+0.44%)	⬆️

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[tony]

addressed by #750