src: compare r2 & kv listing results better

[flakey5]

No description provided.

[cursor]

PR Summary

Low Risk
Changes are limited to background validation/logging of directory listings and should not affect request behavior, but could increase Sentry noise if ordering or metadata differs unexpectedly.

Overview
Tightens the temporary R2Provider.readDirectory cross-check between the S3/cached listing and KvProvider by replacing a full JSON.stringify equality check with targeted validations.

The comparison now handles missing directories explicitly and reports more specific mismatches (hasIndexHtmlFile, subdirectory lists, file count, and per-file name/size), while implicitly tolerating minor lastModified timestamp differences.

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[flakey5]

requesting fast track so we can get actually accurate errors on if there's any significant mismatch between r2 & kv