[roll] Roll fuchsia [inspect] Cap string ref count and add automated rollback safety

- Cap string reference count to MAX_REFERENCE_COUNT (0xFFFFFF) and
  return Err(InvalidReferenceCount) on overflow.
- Introduce PendingStringReference RAII wrapper to automate rollback
  of string reference allocations on failure.
- Clean up manual rollback logic in state.rs using PendingValueBlock
  and PendingStringReference.
- Change unreachable! in delete_value parent check to return
  Err(Error::InvalidBlockType) to avoid panics.

Original-Original-Bug: 498631346
Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1640521
Original-Original-Revision: 4aaef9900305a55b41b64f45c6bd80aaa950bedd
GitOrigin-RevId: 27b0ef849b1a2e278248ce639cc3dd68b3ec7cc4
Change-Id: Ied24fa83a98fb422ac1c32849c86f7369c00da8c
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1644294
Cr-Commit-Position: refs/heads/main@{#194375}