feat(cache/unstable): improve LruCache ejection callbacks and add peek()

[tomas-zijdemans]

• onEject callback now receives a reason parameter ("evicted", "deleted", or "cleared") so callers can distinguish why an entry was removed.
• New peek() method for reading a value without promoting it.
• has() no longer promotes entries in the eviction order
• Constructor validates maxSize, rejecting zero, negative, non-integer, and non-finite values.
• maxSize is now a readonly getter backed by a private field.
• onEject callback is now optional, and clear() calls it for every entry
• calling set, delete, or clear inside an onEject callback throws instead of corrupting state.
• delete() returns false immediately for non-existent keys and fires onEject only after the entry is fully removed.
• Test coverage improved.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.02%. Comparing base (6df7f21) to head (2eae12c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7047   +/-   ##
=======================================
  Coverage   94.01%   94.02%           
=======================================
  Files         627      627           
  Lines       50029    50087   +58     
  Branches     8807     8823   +16     
=======================================
+ Hits        47037    47094   +57     
  Misses       2413     2413           
- Partials      579      580    +1     

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