[BUG] Reset role blocks when model.reset is called

[hudson-ai]

Just empties the dict of open role blocks when model.reset is called. Should close #1071

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 63.98%. Comparing base (11892c2) to head (b3ef384).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
guidance/models/_model.py	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1073      +/-   ##
==========================================
- Coverage   65.35%   63.98%   -1.37%     
==========================================
  Files          65       65              
  Lines        4892     4893       +1     
==========================================
- Hits         3197     3131      -66     
- Misses       1695     1762      +67     

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[nopdive]

LGTM.