refactor: clean up shared feature helpers

[jderochervlk]

Tracking issue: #342

Stack context

Part 30 of the Option 5 folder-feature stack.

• Previous: refactor: establish Window folder feature #339
• Next: feature-graph guardrails and final documentation

Review this PR as the incremental diff against #339.

Summary

• split cache-specific support types into internal src/storage/CacheTypes.res
• return WebWorkersTypes to the Workers folder
• update Cache, CacheStorage, Window, browser globals, and worker scopes to use the owning helper modules
• fold the shared Blob/File type identity into foundational DOM.res
• remove the internal BaseFile helper while preserving FileTypes.blob and FileTypes.file aliases

Why this cleanup is last

Earlier PRs temporarily kept WebWorkersTypes with Storage and BaseFile in core so folder moves could remain mechanical. With the complete graph in place, the ownership directions are now explicit: Workers depends on Storage, and File aliases the small foundational identities in DOM.

Resolved temporary state

• cache and worker support types no longer share one misplaced helper module
• the standalone BaseFile module is removed
• no module-slice exception is required

Review focus

• preservation of Blob/File type identity through the new DOM aliases
• cache/worker helper ownership
• the unchanged public feature closures

Verification

• node_modules/.bin/rescript build --prod --features WebAPI.DOM
• node_modules/.bin/rescript build --prod --features WebAPI.Storage
• node_modules/.bin/rescript build --prod --features WebAPI.Workers
• node_modules/.bin/rescript build --prod --features WebAPI.Window
• npm run build
• npm test
• npm run format:check
• git diff --check

[jderochervlk]

@codex

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Chef's kiss.

Reviewed commit: 6aad67b61d

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