Implement create_empty and create_empty_like convenience methods for Dataset creation.

[dmitriyrepin]

#687
Redone without any code reuse.

[codecov]

Codecov Report

❌ Patch coverage is 91.78082% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.67%. Comparing base (c3ba558) to head (c89f7e2).
⚠️ Report is 211 commits behind head on main.

Files with missing lines	Patch %	Lines
src/mdio/api/create.py	73.43%	6 Missing and 11 partials ⚠️
tests/integration/test_z_create_empty.py	97.26%	1 Missing and 4 partials ⚠️
tests/integration/testing_helpers.py	95.55%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #736      +/-   ##
==========================================
+ Coverage   85.30%   87.67%   +2.36%     
==========================================
  Files          46       89      +43     
  Lines        2219     5096    +2877     
  Branches      306      345      +39     
==========================================
+ Hits         1893     4468    +2575     
- Misses        281      541     +260     
- Partials       45       87      +42     

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