chore: upgrade mega-evm to v1.5.0 & bump version to v2.0.9

[flyq]

Summary

Upgrade mega-evm dependency from v1.4.1 to v1.5.0 and bump workspace version to 2.0.9.

Changes

• Update mega-evm git dependency from rev = "v1.4.1" to rev = "v1.5.0" in workspace Cargo.toml
• Bump workspace package version from 2.0.8 to 2.0.9
• Update Cargo.lock to reflect new mega-evm (1.5.0) and mega-system-contracts (1.5.0) versions

Test plan

• cargo check passes with the new dependency
• cargo test passes — no breaking API changes from mega-evm upgrade
• cargo clippy --workspace --all-targets --all-features has no new warnings

[claude]

This PR has no labels applied. It is a dependency upgrade and version bump (a maintenance/chore task), so it does not fit most available labels. The closest available label would be enhancement ("Improvements or additions"), though a dedicated chore or dependencies label would be more precise. Consider adding enhancement or creating a more appropriate label for this type of change.

[claude]

The mechanical changes look correct (lock file hash, version bump). One question before approving:

What changed in mega-evm v1.5.0? The PR description says there are no breaking API changes but doesn't explain what the upgrade actually contains (bug fixes, new EVM opcodes, execution logic changes, etc.). For a dependency that's at the heart of block execution correctness, reviewers need to understand the scope of the change to sign off confidently. A brief changelog summary or link to the mega-evm v1.5.0 release/tag would help.