fix: broken cache

[SAHU-01]

Title

Fixes: #861

Description

The service worker was always storing responses in the mutable cache, regardless of protocol type (IPFS vs IPNS).

• Modified fetchAndUpdateCache() to accept isMutable as a parameter
• Updated getResponseFromCacheOrFetch() to pass the correct isMutable value based on protocol:
  • isMutable = true for IPNS (mutable content)
  • isMutable = false for IPFS (immutable content)
• Now cache lookup and storage use the same cache for each protocol

Notes & open questions

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works

Reviewer: @SgtPooki