Fix net_version

[DmytroNazarenko]

This fix is making net_version JSON RPC call compatible with Ethereum one:
https://ethereum.org/en/developers/docs/apis/json-rpc/#net_version

net_version will return decimal number, not hex string. Example:

> curl -X POST --data '{"jsonrpc":"2.0","method":"net_version","params":[],"id":67}' ...
> {"id":67,"jsonrpc":"2.0","result":"4660"}

Tests:

• Added unit test
• Tested on local setup

[github-actions]

SUGGESTIONS BEFORE MERGE:

1. Build custom container here: https://github.com/skalenetwork/skaled/actions?query=workflow%3A%22Custom+Docker+and+Binary%22
2. Test it here: https://github.com/skalenetwork/skale-ci-integration_tests/actions?query=workflow%3A%22Skaled+Nightly+Tests%22
3. Edit VERSION file appropriately to your changes!
   See https://skalelabs.atlassian.net/wiki/spaces/SKALE/pages/2444951553/Branching+instructions

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (v3.17.2@e412fa1). Click here to learn what that means.
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Additional details and impacted files

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