Add StakingPrecompileV2

[ales-otf]

Description

Recently we changed some methods in StakingPrecompile to conform the amount precisions to our Substrate API. They were in ETH-precision before. But that affected some users.

This PR takes back ETH-precisions to those methods and introduces a new version of StakingPrecompile, that has API consistent with our Substrate API.

Tests are here: opentensor/subtensor-js-tests#12

Related Issue(s)

• Closes #[issue number]

Type of Change

• 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

• StakingPrecompile exists only for backward compatibility from now on and considered deprecated (replaced by StakingPrecompileV2 at a new address)
• StakingPrecompile::get_stake now again returns the amount, converted to ETH-precision
• StakingPrecompile::remove_stake accepts amount in ETH-precision as it was before

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]

need set the valid value.

[ales-otf]

This is not used in the new version, so I set it to 0s (as in Metagraph and Ed25519Verify contracts). But I now think, it's better to change this value to Option<[u8; 32]> in the trait, to prevent potential mistakes.

[ales-otf]

Done.

[ales-otf]

Even better would be ridding of this constant and using a conversion from the contract's address. Just look at this value is hard to understand whether it came from the contract address or not. Would be good to have a method in PrecompileExt trait and use Self::INDEX to generate this value on-demand. Will introduce a little runtime overhead, but that would be a lot more sound.

[open-junius]

looks great.