[roll] Roll fuchsia [storage][fscrypt] Introduce iterator-based hashing and CasefoldStr improvements

Implements a more consistent Unicode normalization interface around
CasefoldString and CasefoldStr, and updates tea_hash_filename to accept
iterators (impl IntoIterator<Item = u8>) instead of byte slices.

This allows hashing to be performed directly on iterators, avoiding
unnecessary allocations of temporary String or Vec<u8> objects when
normalizing and casefolding filenames.

This is a prerequisite for improving casefold support in Fxfs and
Starnix.

Test: fx build (verifies compilation of libraries and consumers)
TAG: agy
CONV: 2afb3abf-d60e-4491-a29f-cefa1f015249
Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1676284
Original-Original-Revision: 7f6c4c38c1bf2ffcebdea5c1acfb8ab1a19cd41e
GitOrigin-RevId: 2ab69d95369201c94a14b8ae33f2e79792694ed6
Change-Id: Ib9b7d27e717b68f1b1daa3ac202b24cf72599bdb
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1680339
Cr-Commit-Position: refs/heads/main@{#195563}