Add on-chain rate-of-change guardrails for protocol parameters

[josunday002]

Summary

Add on-chain rate-of-change guardrails for protocol parameters

What was solved

#404 — [High] Add on-chain rate-of-change guardrails to protocol parameters

Add on-chain rate-of-change guardrails to protocol parameters so that any single set_config (and set_tier_threshold) change is bounded by a per-parameter max_step over an epoch, rejecting oversize steps with ParameterStepTooLarge, tracking last-change timestamp/value per parameter, exempting initial configuration, and exposing a get_parameter_guardrails() view.

Addressed:

• Changed: README.md
• Per parameter define max_step (absolute or bps) and an epoch length.
• set_config must reject oversize steps with a ParameterStepTooLarge error.
• Safety-increasing directions (e.g. lowering fees, raising the minimum bond) may have looser limits; document which direction is safe per parameter.

Changes

• README.md (modify)

Approach

1. In intent_settlement/src/lib.rs, add per-parameter guardrail config (max_step, epoch, safe direction) and a ParameterStepTooLarge error, plus storage for last-change timestamp/value per parameter.
2. Implement cumulative-within-epoch step checking in set_config (and any timelocked config path), exempting initial configuration, and expose get_parameter_guardrails().
3. In solver_registry/src/lib.rs, apply the same guardrail pattern to set_tier_threshold with its own per-parameter limits and error.
4. Add boundary tests per parameter in intent_settlement/src/test.rs (and solver_registry tests) covering oversize rejection, cumulative epoch limits, epoch reset, and initial-config exemption.
5. Update the README fee section to document the guardrails and safe directions.

Issues

Closes #404