call validate in pre_dispatch to have same validations

[ParthDesai]

Description

This PR fixes a bug in the runtime which can allow malicious block author to include invalid txs in a block. It fixes the issue by doing the same checks as validate in pre_dispatch method of SubtensorSignedExtension.

The inclusion of same checks in pre_dispatch mean that the checks are being run during Executive::apply_extrinsic when the block is being executed against the current state.

Related Issue(s)

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

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)

Additional Notes

[sam0x17]

please change this to merge into devnet-ready ;)

[ParthDesai]

please change this to merge into devnet-ready ;)

Done and rebased to devnet-ready. @sam0x17