refactor(fracmanager): move name generation and sealing logic to FractionProvider

[eguguchkin]

Fixes #155

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• I have read and followed all requirements in CONTRIBUTING.md;
• I used LLM/AI assistance to make this pull request;

[codecov-commenter]

Codecov Report

❌ Patch coverage is 78.33333% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.07%. Comparing base (2daa556) to head (3476114).

Files with missing lines	Patch %	Lines
fracmanager/fraction_provider.go	67.56%	8 Missing and 4 partials ⚠️
fracmanager/fracmanager.go	95.23%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #176      +/-   ##
==========================================
+ Coverage   71.06%   71.07%   +0.01%     
==========================================
  Files         198      198              
  Lines       18219    18232      +13     
==========================================
+ Hits        12947    12959      +12     
+ Misses       4552     4544       -8     
- Partials      720      729       +9     

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