Build: Bump fsspec from 2026.2.0 to 2026.4.0

Bumps [fsspec](https://github.com/fsspec/filesystem_spec) from 2026.2.0 to 2026.4.0.
- [Commits](fsspec/filesystem_spec@2026.2.0...2026.4.0)

---
updated-dependencies:
- dependency-name: fsspec
  dependency-version: 2026.4.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]