Follow-up: Split assetService.ts into focused modules (hash helpers, abort utilities, public-inclusive input cache)

## Context

Identified as a follow-up item in PR #11873.

## Problem

`assetService.ts` has grown to encompass hash helpers (`isBlake3AssetHash`, `toBlake3AssetHash`, `checkAssetHash`), abort utilities, the public-inclusive input asset cache (`getInputAssetsIncludingPublic`, `invalidateInputAssetsIncludingPublic`), and the core asset CRUD operations. This makes the module harder to navigate and test in isolation.

## Proposed Work

Consider splitting `assetService.ts` into more focused sub-modules, for example:
- Hash helpers and `checkAssetHash`
- Abort/shared-load utilities
- Public-inclusive input asset cache
- Core asset CRUD

## References

- PR: https://github.com/Comfy-Org/ComfyUI_frontend/pull/11873
- Requested by: @jaeone94

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-11881-Follow-up-Split-assetService-ts-into-focused-modules-hash-helpers-abort-utilities--3566d73d36508121aeabf3753469565d) by [Unito](https://www.unito.io)