chore: add nv28 skeleton

[rjan90]

Depends on: filecoin-project/ref-fvm#2220 and a new ref-fvm release. Once that is out, will update the lock file.

Closes: #547

[Copilot]

Pull Request Overview

This PR adds skeleton support for network version 28 (nv28) by updating the FVM engine version mapping and upgrading FVM dependencies. The changes prepare the codebase for nv28 compatibility while maintaining backward compatibility with existing network versions.

• Updated engine version mapping to include network version 28 in the V3 engine range
• Upgraded FVM dependencies from version 4.7.3 to 4.7.4 with nv28-dev feature enabled

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
rust/src/fvm/engine.rs	Extended V3 engine version range to include network version 28
rust/Cargo.toml	Updated FVM package versions and added nv28-dev feature flag

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