use uint64 for number flags

[libotony]

Description

This is a minor improvement of the flags parsing component.

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my 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] New and existing E2E tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules
• [x] I have not added any vulnerable dependencies to my code

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 31 lines in your changes missing coverage. Please review.

Project coverage is 62.50%. Comparing base (5d05048) to head (0aa0527). Report is 1 commits behind head on master.

Files	Patch %	Lines
cmd/thor/main.go	0.00%	24 Missing :warning:
cmd/thor/utils.go	0.00%	7 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #779 +/- ## ========================================== - Coverage 62.54% 62.50% -0.05% ========================================== Files 199 199 Lines 18140 18153 +13 ========================================== Hits 11346 11346 - Misses 5710 5723 +13 Partials 1084 1084 ```

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