Target place for backlog

[h1alexbel]

closes #96

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PR-Codex overview

This PR focuses on adding support for Backlog in the Tracehub project. It includes the following changes:

• Added Backlog interface
• Implemented YmlBacklog class for YAML-based backlogs
• Updated Project interface to include backlog() method
• Updated relevant test classes to include tests for backlog functionality

The following files were skipped due to too many changes: src/main/java/git/tracehub/facts/ExecOn.java, src/test/java/git/tracehub/agents/YmlBacklogTest.java, src/main/java/git/tracehub/agents/github/GhOrder.java, src/test/java/git/tracehub/facts/ExecOnTest.java, src/main/java/git/tracehub/tk/TkGitHub.java, src/test/java/git/tracehub/agents/github/GhOrderTest.java

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3f1c4bb) 80.58% compared to head (81e3d68) 81.35%.
Report is 15 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #103      +/-   ##
============================================
+ Coverage     80.58%   81.35%   +0.76%     
- Complexity       96      104       +8     
============================================
  Files            32       35       +3     
  Lines           340      354      +14     
  Branches         19       19              
============================================
+ Hits            274      288      +14     
  Misses           59       59              
  Partials          7        7              

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[h1alexbel]

@rultor merge

[h1alexbel]

@rultor merge

[h1alexbel]

@rultor merge

[h1alexbel]

@rultor status