refactor: remove unsafe sync functions

[mdjastrzebski]

Summary

Removes all unsafe sync functions from the public API:

• unsafe_act
• unsafe_renderSync
• unsafe_fireEventSync
• unsafe_renderHookSync

These functions were deprecated in favor of their async counterparts (act, render, fireEvent, renderHook). All tests and documentation updated.

Test plan

• All tests pass (yarn test, yarn typecheck)
• Removed functions are no longer accessible from public API
• Migration guide updated with breaking change documentation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.10%. Comparing base (2f582ac) to head (7d0cc8a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1855      +/-   ##
==========================================
- Coverage   91.23%   91.10%   -0.14%     
==========================================
  Files          93       92       -1     
  Lines        5432     5215     -217     
  Branches      907      869      -38     
==========================================
- Hits         4956     4751     -205     
+ Misses        471      459      -12     
  Partials        5        5              

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