fix: `Account.isValidPair` throwing on invalid seeds

[sno2]

Description

The issue was that Account.isValidPair was throwing errors when the seed inputs were not of valid lengths or were not actual hex characters. This PR fixes that issue and implements tests to ensure this behavior stays fixed.

Fixes #151

Type of change

• [ ] Chore (chore: description-of-task)
• [x] Fix (fix: description-of-fix)
• [ ] Feature (feat: description-of-fix)
• [ ] Test (test: description-of-tests-performed)
• [ ] Docs (docs: description-of-docs-added-or-modified)
• [ ] Refactor (refactor: description-of-refactor)

Please specify the type of change in your title following the above format

Checklist:

• [x] My code follows the style guidelines of this project
• [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
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules

[zinoadidi]

@sno2 your account number #tnbc

[sno2]

@sno2 your account number #tnbc

d84543947090d300910f8d1b9604c0c0a56fafca6cfbe52511c1e31757188bca Thanks