[Chore] refactor test-cli.py to test init, diagnose and run commands

[kentwelcome]

PR checklist

• [x] Ensure you have added or ran the appropriate tests for your PR.
• [x] DCO signed

What type of PR is this? Unit Test

What this PR does / why we need it:

• Add unit test for CLi to test init, diagnose and run commands
• Fix some path related issues
  • Currently, duckDB will only search the db file from CWD. After this fix, we will search CWD first and search working_dir secondly.
  • When we use --dbt-project-dir to config dbt project dir, the method load_dbt_project will use a wrong path to load file.

Which issue(s) this PR fixes: N/A

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov[bot]]

Codecov Report

Merging #837 (6893c4a) into main (dc17836) will increase coverage by 10.77%. The diff coverage is 37.50%.

@@             Coverage Diff             @@
##             main     #837       +/-   ##
===========================================
+ Coverage   34.56%   45.34%   +10.77%     
===========================================
  Files          68       68               
  Lines        9761     9766        +5     
===========================================
+ Hits         3374     4428     +1054     
+ Misses       6387     5338     -1049     

Files Changed	Coverage Δ
piperider_cli/datasource/duckdb.py	27.86% <16.66%> (+1.46%)	:arrow_up:
piperider_cli/dbtutil.py	69.10% <100.00%> (+9.10%)	:arrow_up:

... and 18 files with indirect coverage changes

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