Add __repr__ and _repr_html_ to builder and template

[BrianMichell]

Adds string and HTML representation of key builder classes.

[codecov]

Codecov Report

❌ Patch coverage is 29.25170% with 104 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.95%. Comparing base (c3ba558) to head (350894e).
⚠️ Report is 198 commits behind head on main.

Files with missing lines	Patch %	Lines
src/mdio/builder/formatting_html.py	24.16%	91 Missing ⚠️
src/mdio/builder/dataset_builder.py	37.50%	5 Missing ⚠️
src/mdio/builder/templates/base.py	50.00%	4 Missing and 1 partial ⚠️
src/mdio/builder/template_registry.py	50.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #719      +/-   ##
==========================================
+ Coverage   85.30%   86.95%   +1.64%     
==========================================
  Files          46       86      +40     
  Lines        2219     4790    +2571     
  Branches      306      317      +11     
==========================================
+ Hits         1893     4165    +2272     
- Misses        281      553     +272     
- Partials       45       72      +27     

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