fix(deduplicate): do not deduplicate non-safe methods by default

[mcollina]

Summary

• fix deduplicate interceptor to gate deduplication with methods.includes(opts.method)
• prevent non-safe methods (like POST) from entering deduplication when using default options
• add a regression test that verifies concurrent POST requests are not deduplicated by default

Fixes #4817.

Testing

• npx borp -p "test/interceptors/deduplicate.js"

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.25%. Comparing base (b3326b5) to head (32c8aca).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4818   +/-   ##
=======================================
  Coverage   93.25%   93.25%           
=======================================
  Files         109      109           
  Lines       34153    34151    -2     
=======================================
  Hits        31848    31848           
+ Misses       2305     2303    -2     

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