fix(cnight-observation): complete CIP-19 validation for Cardano reward addresses (#498)

[m2ux]

Summary

Consolidate Cardano reward-address (CIP-19) validation into a single validated constructor for CardanoRewardAddressBytes, and route the follower, genesis config, and the mapping-address setter through it so malformed, wrong-length, wrong-type, or wrong-network reward addresses are rejected with specific errors.

🐛 Issue 📐 Engineering

Jira: PM-20267

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Motivation

Cardano reward addresses supplied to the cNIGHT observation path are currently validated only partially, and in several independent places. Malformed, wrong-length, wrong-address-type, or wrong-network reward addresses can pass through the follower, the genesis config, and set_mapping_validator_contract_address, and the follower carries roughly three ad-hoc parsing spots each with its own error enum. An address that is not a valid CIP-19 reward address for the expected network can therefore be accepted and stored, misdirecting or silently dropping rewards and making failures hard to diagnose.

This change gives every entry point one strict, shared check that rejects each bad case with a specific, named error, replacing the scattered ad-hoc parsing with a single validated constructor and error type.

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Changes

• Primitive — adds a validated constructor CardanoRewardAddressBytes::try_new(bytes, expected_network) and a dedicated error type with a distinct variant per rejection case (wrong length, wrong address type, wrong network), checking length first then the CIP-19 header nibbles via no_std bit arithmetic; the length-only conversion is retained for test and benchmark use.
• Follower — the four reward-address sites (registration, deregistration, asset-create, asset-spend) share one infallible constructor that builds the reward address from the stake credential and the configured network. There is no follower-side validation or rejection, because a reward address the node constructs from an already-valid credential cannot be malformed; the now-dead reward-address error variant is removed.
• Genesis — validates deserialized reward-address keys against address type and expected network during the genesis build, where the network is available, rather than the length-only check used previously.
• Mapping validator — gives set_mapping_validator_contract_address and the genesis validator-address build a sibling validated path returning a specific error, kept separate from the reward-address constructor because the validator address is a different Cardano address category.
• Tests — cover each rejection case (wrong length, wrong type, wrong network, malformed header) plus valid type-14 and type-15 round-trips, and repair the existing genesis/extrinsic tests for the new validation.
• On-chain rejection event — not added. The follower filters invalid reward addresses before the inherent, so the pallet never observes a rejected registration; the per-rejection follower log provides the intended observability without a non-trivial inherent-payload change.

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📌 Submission Checklist

• Changes are backward-compatible (or flagged if breaking)
• Pull request description explains why the change is needed
• Self-reviewed the diff
• I have included a change file, or skipped for this reason: [reason]
• If the changes introduce a new feature, I have bumped the node minor version
• Update documentation (if relevant)
• No new todos introduced

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🔱 Fork Strategy

• Node Runtime Update
• Node Client Update
• Other
• N/A

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🗹 TODO before merging

• Run and pass cargo check / cargo clippy / cargo nextest (deferred — see Validation status)
• Ready for review

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