[rust-launcher] Use DockerSha256Digest type for ManifestEntry::digest #2611
Description
Context
Follow-up from PR #2326 (port node launcher to Rust). Tracked in #2598.
Problem
In crates/tee-launcher/src/docker_types.rs (line 33), ManifestEntry::digest is String while ManifestConfig::digest correctly uses DockerSha256Digest. This inconsistency could allow malformed digests to propagate undetected.
Action
Change ManifestEntry::digest from String to DockerSha256Digest and fix any downstream code that relies on the string representation.