Update target-specific dependency versions during release

[lukidoescode]

Context

The UpdateDependencyVersionsStep introduced in #56 covers [dependencies], [dev-dependencies], [build-dependencies], and [workspace.dependencies] sections.

Problem

[target.'cfg(...)'.dependencies] sections are not yet covered. If an intra-workspace dependency is declared under a target-specific section with an explicit version, it will not be updated during release.

Expected Behaviour

After a release, version constraints in target-specific dependency sections that reference released crates should also be updated.

Notes

• Target-specific deps are rare for intra-workspace references, so this is lower priority
• The TOML traversal is more complex because target keys use arbitrary cfg expressions as keys (e.g., target.'cfg(target_os = "linux")')
• The implementation should follow the same pattern as the standard dependency update step