fix(cache): Cache.add() and Cache.addAll() hang for responses with bodies

[marko1olo]

Problem

Cache.add() and Cache.addAll() deadlock when the response has a body: the spec requires the implementation to read the response body before storing it, but the current code never drains the original stream, so the promise never settles.

Fix

Clone the response before storing (so the original body can be consumed independently), and explicitly drain the original stream after the clone is created.

Tests

Added test/cache/cache-add-body.js — all pass (node --test test/cache/cache-add-body.js).

Split from #5626 as requested by @mcollina.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.86%. Comparing base (2ab178a) to head (13ef5fd).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/web/cache/cache.js	92.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5627      +/-   ##
==========================================
+ Coverage   93.50%   93.86%   +0.35%     
==========================================
  Files         110      110              
  Lines       38455    38484      +29     
==========================================
+ Hits        35959    36122     +163     
+ Misses       2496     2362     -134     

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