Add fast-blocks feature to node

[ales-otf]

Description

This PR configures fast-blocks feature for the node-subtensor crate. Without it you can't just cargo run the node with fast-blocks - you need to build the runtime with fast-blocks first. With this feature, you can run the node with:

cargo run -p node-subtensor --features fast-blocks -- --dev

Related Issue(s)

• Closes cargo run should run the node #977

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):

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