Fix incorrect regex for integer literals

[ef3d0c3e]

I recently noticed that the regex responsible for parsing integer literals doesn't work as expected.
The prefix part of the regex matches for [bBxX]* which caused any combination of bBxX to be matched, instead of only matching repeating sequences: https://regex101.com/r/5lUQ0U/1

In cases like 0xb0b; 0xb is considered the prefix of the integer literal, causing the last b to be matched as an invalid suffix.

In the modified regex combinations can no longer match, only repetitions are allowed: https://regex101.com/r/nWkXWv/1

I'm not sure about how to run tests. The tests seems to fail on the current master branch. With more information, I might be able to add tests for this modified regex.

Verification Steps

Please ensure the following steps have been completed:

• Added new tests to cover the changes.
• Fixed all broken tests.
• Ran poetry run flake8 to check for linting issues.
• Verified that all unit tests are passing:
  • Ran poetry run pytest to ensure unit tests pass.
  • Ran poetry run tox to validate compatibility across Python versions.