fix: coin98 wallet add signMessage method

[khiemsoft]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Checklist:

• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings

Type of change.

• [x] FIX - a PR of this type patches a bug.
• [ ] FEATURE - a PR of this type introduces a new feature.
• [ ] BUILD - a PR of this type introduces build changes.
• [ ] CI - a PR of this type introduces CI changes.
• [ ] DOCS - a PR of this type introduces DOCS improvement.
• [ ] STYLE - a PR of this type introduces style changes.
• [ ] REFACTOR - a PR of this type introduces refactoring.
• [ ] PERFORMANCE - a PR of this type introduces performance changes.
• [ ] TEST - a PR of this type adds more tests.
• [ ] CHORE - a PR introduces other changes than the specified above.

[trechriron]

Please make a template selection above, fill in the details, and mark the appropriate checkboxes. Thanks!

[trechriron]

@khiemsoft - did you see my request for changes?

[khiemsoft]

@khiemsoft - did you see my request for changes?

Hi, I just fixed this warning. Please verify it. Thanks for your support.