fix decryption key padding for ed25519

[himanshuchawla009]

Added padding to decryption key which is used to decrypt ed25519 seed.

Motivation and Context

Saw some e2e test failing randomly, found out its happening because of unpadded key.
Jira Link:

Screenshots (if appropriate):

Types of changes

• 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)

Checklist:

• My code follows the code style of this project. (run lint)
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[chaitanyapotti]

lgtm