feat(ethexe): add Router.protocolVersion to contracts & client

[StackOverflowExcept1on]

Closes #5440

Summary

This PR adds ability to update protocol version on Router and creates corresponding event that makes graceful join on nodes if version does not match, and also check of protocol version before creation has been added to client constructor.

How to test

cargo build --package ethexe-cli
./target/debug/ethexe run --dev --validators-malachite-pub-keys file.json
cast  send \
  0xCf7Ed3AccA5a467e9e704C703E8D87F634fB0Fc9 \
  "function bumpProtocolVersion(uint256 newProtocolVersion) external" \
  --private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80

2026-05-30T19:57:29.430684Z  INFO ethexe_service: 📦 receive a chain head height=49 timestamp=1780171049 hash=0x9aba…733f parent_hash=0x27ef…b7e3
2026-05-30T19:57:29.433978Z  INFO ethexe_service: Observer requested graceful shutdown: Client protocol version mismatch. Expected 1, got 2. Please make sure to use compatible version of Ethereum client with `Router` contract.

Checklist

• PR title follows Conventional Commits (type(scope): description)
• Single logical change
• Tests added or updated (if logic changed)
• Docs updated (if needed)

[gemini-code-assist]

Warning

Gemini encountered an error creating the summary. You can try again by commenting /gemini summary.

[breathx]

Remove hard pin to specific version and allow any compatible + bump only version