fix #3114: prevent scientific notation when generating bank account number

[AhmedHisham552]

Motivation / Background

This Pull Request has been created to fix issue #3114, a bug in Faker::Bank.account_number where generated values could sometimes include scientific notation (e.g., 3512553848424886e-05) due to using rand.to_s[2..].

This resulted in invalid bank account numbers containing non-digit characters.

The new implementation ensures that account numbers always consist of digits only.

Additional information

• The fix uses integer-based digit generation, avoiding reliance on stringified floats.

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug, refactor something, or add a feature.
• Tests and Rubocop are passing before submitting your proposed changes.

If you're proposing a new generator or locale:

• Double-check the existing generators documentation to make sure the new generator you want to add doesn't already exist.
• You've reviewed and followed the Contributing guidelines.

[jremes-foss]

LGTM ✅