chore: retire cache after its move to Appwrite

[ChiragAgg5k]

Cache now lives in Appwrite following appwrite/appwrite#13899. Remove packages/cache so this repository stops discovering and publishing it during Split runs. Refresh the local dependency graph and list cache with the packages maintained in Appwrite.

domains and vcs here still require utopia-php/cache: ^4.0 || ^5.0; they now resolve it from Packagist, which the mirror keeps serving, so no constraint changes.

Validation: bin/monorepo validate and git diff --check pass.

Appwrite merged #13899 as a merge commit, and its post-merge Split pushed cache: the mirror head is the merge of #13899, and its tree daa6f4e exactly matches Appwrite's packages/cache. (That Split run is marked failed only because the locale mirror still has classic branch protection rejecting the split app; cache itself pushed.) After merge, confirm this repository's Split no longer includes cache.

Still open against the old copy: #279 (perf(cache): reuse the decoded envelope while the stored string is unchanged), which needs re-opening against packages/cache in Appwrite or closing. The mirror has 6 open issues and PRs, triaged in the Appwrite PR body.

Part of appwrite/appwrite#13828.

[walter-o-brien]

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