Treat burn address as invalid when added as contact

### What is this about?

When adding `0x000000000000000000000000000000000000dEaD` as a contact it is currently not flagged as invalid.

Validation for this address already exists within the Send flow `ui/pages/confirmations/utils/sendValidations.ts`. Contacts relies on a legacy send util that does not define the burnaddress. `shared/modules/hexstring-utils.ts`

Update Contact address validation to use the sendValidation.

### Scenario

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### Design

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### Technical Details

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### Threat Modeling Framework

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### Acceptance Criteria

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### Stakeholder review needed before the work gets merged

- [ ] Engineering (needed in most cases)
- [ ] Design
- [ ] Product
- [ ] QA (automation tests are required to pass before merging PRs but not all changes are covered by automation tests - please review if QA is needed beyond automation tests)
- [ ] Security
- [ ] Legal
- [ ] Marketing
- [ ] Management (please specify)
- [ ] Other (please specify)

### References

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Start with shared/modules/hexstring-utils.ts and compare its legacy contact validation with ui/pages/confirmations/utils/sendValidations.ts. Trace the contact address validation path, update it to use the send validation, and verify that adding 0x000000000000000000000000000000000000dEaD as a contact is rejected.

Written by the indexing model from the issue text.