feat(cache): expose cache property on memoized functions

[tomas-zijdemans]

Exposed the cache as a public property so callers can inspect or manually invalidate the cache (e.g. fn.cache.delete(...), fn.cache.clear()).

Changed MemoizationCache from type alias to interface to align with the style guide

Removed unused import and dropped the lint suppression.

Replaced the cache.has(key) + cache.get(key)! two-step lookup with a single cache.get(key) call. This avoids a redundant lookup on every cache hit.

Simplified tests a lot, maintaining coverage

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.01%. Comparing base (6df7f21) to head (86ce23c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7045      +/-   ##
==========================================
- Coverage   94.01%   94.01%   -0.01%     
==========================================
  Files         627      627              
  Lines       50029    50030       +1     
  Branches     8807     8807              
==========================================
  Hits        47037    47037              
  Misses       2413     2413              
- Partials      579      580       +1     

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