[roll] Roll fuchsia [assembly] Migrate product_bundle to strongly typed errors

Migrate the `product_bundle` crate from generic `anyhow::Error` to
strongly typed errors using `thiserror`. This improves error handling
and allows callers to match on specific errors.

In `v2.rs`:
- Define `CanonicalizeError` for path manipulation failures.
- Define `V2Error` wrapping `fuchsia_repo::repository::Error` to
  preserve external error types.
- Make `from_str` and canonicalization methods infallible where
  possible.

In `product_bundle.rs`:
- Define `ProductBundleLoadError` (incorporating `CanonicalizeError`).
- Define `ProductBundleWriteError` and `ProductBundleExtractError`.
- Keep `ProductBundle::try_load_from` returning `anyhow::Result` at
  the boundary to avoid churn in external callers.

In `product_bundle_builder.rs`:
- Define `ProductBundleBuildError`, preserving `anyhow::Error` as
  sources where needed.

Update callers in `plugins/target/update` and
`plugins/product_bundle/create` to handle the new types.

Test: Verified by successful build of the workspace. No new tests added
as behavior is unchanged.

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1592230
Original-Revision: cec0bbdd2cf551d2821110242ed11a1643f9f2c3
GitOrigin-RevId: 2d3326e72186da6f791cdc9813a7794cbcf0e1b2
Change-Id: I07a0525c02d3826557303ae9f1dcd01729fd4b6f