refactor: Simplify NPM fetching logic

[FrederikBolding]

Description

Simplify the NPM fetching implementation to make it more readable, while also fixing a couple of issues:

• Use the cache directory for the app instead of a shared directory
• Re-use the cache key for the unpacked directory to allow for multiple installs at a time
• Properly clean up files on the filesystem after install
• Match error messages and states from the extension implementation

Changelog

CHANGELOG entry: null

Related issues

Closes: MetaMask/snaps#3617

---

Note

Refactors NPM tarball fetching with direct blob fetch, status/size validation, improved error handling, and robust cleanup; updates tests to match.

• Core (NPM fetch):
  • Rewrite NpmLocation.fetchNpmTarball to use ReactNativeBlobUtil.config({ appendExt: 'tgz' }).fetch and RNTar.unTar.
  • Add response validation: assert 404 not-found, require 200 OK, enforce content-length against TARBALL_SIZE_SAFETY_LIMIT.
  • Improve errors using getErrorMessage; accept DetectSnapLocationOptions via constructor.
  • Ensure cleanup in finally: response.flush() and fs.unlink of unpacked path.
  • Read files as UTF-8 strings in readAndParseAt; remove stringToBytes.
  • Remove helpers: decompressFile, fetchAndStoreNPMPackage, cleanupFileSystem; drop SNAPS_NPM_LOG_TAG.
• Tests:
  • Update mocks to include respInfo with status and content-length; adjust FS mocks; align with new fetch/untar flow.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
92.9% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[metamaskbot]

Missing release label release-7.58.0 on PR. Adding release label release-7.58.0 on PR and removing other release labels(release-7.59.0), as PR was added to branch 7.58.0 when release was cut.