Refactor rate limits

[shamil-gadelshin]

Description

This PR migrates obsolete rate limits into the existing map LastRateLimitedBlock:

• TxDelegateTakeRateLimit
• TxChildkeyTakeRateLimit
• TxRateLimit
• NetworkRateLimit
• ServingRateLimit
• WeightsSetRateLimit

Related Issue(s)

• Closes Cleanup rate limits #1519

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

This PR changes storage maps semantics - default values are zero when requested using the storage RPC. The runtime getters return the previous default values.

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

[shamil-gadelshin]

There will be a second part for this task (after a discussion with @gztensor) for dealing with LastTxBlock, LastTxBlockChildKeyTake, LastTxBlockDelegateTake, etc.

[shamil-gadelshin]

Superseded by #1721