Upgrade Polkadot SDK to stable2412-6

[l0r1s]

Second step of #1594

Description

This PR introduces the update from the Polkadot SDK version stable2409-7 to the stable2412-6.

• Bump substrate dependencies versions

• Convert signed extension to transaction extensions (following FRAME: Reintroduce TransactionExtension as a replacement for SignedExtension paritytech/polkadot-sdk#3685)

• Removed unused CommitmentsSignedExtension

• Fix issues related to frontier update

• Fix type issues/tests

Type of Change

• Upgrade from upstream dependencies
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Breaking Change

If this PR introduces a breaking change, please provide a detailed description of the impact and the migration path for existing applications.

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have run cargo fmt and cargo clippy to ensure my code is formatted and linted correctly
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Screenshots (if applicable)

Please include any relevant screenshots or GIFs that demonstrate the changes made.

Additional Notes

Please provide any additional information or context that may be helpful for reviewers.

[open-junius]

Can't start the node.
user@user-X870-EAGLE-WIFI7:~/github/opentensor/subtensor$ ./target/release/node-subtensor --dev --tmp
Error: Service(Other("Network backend not supported"))
2025-06-13 13:16:08 Subtensor Node
2025-06-13 13:16:08 ✌️ version 4.0.0-dev-984ea2cd613
2025-06-13 13:16:08 ❤️ by Substrate DevHub https://github.com/substrate-developer-hub, 2017-2025
2025-06-13 13:16:08 📋 Chain specification: Bittensor

[open-junius]

need configure network backend libp2p or litep2p.