Lookahead breaks pattern

[alturkovic]

Describe the bug
It seems like negative lookahead breaks the pattern generated by RgxGen.
I am aware that lookaheads have limited support but #63 mentioned in README/limitations does not seem like the same issue to me.
Reporting for awareness.

To Reproduce
Steps to reproduce the behavior:

1. With regex pattern '^(?!(False|True)$)[a-zA-Z_][\w]*$'
2. Use RgxGen.parse(pattern).generate()
3. Get results such as: yl[>B4BemOeLW2QQsNUPKtExdhKDwkroNwAptvhYx

Expected behavior
Any alphanumeric+underscore string starting with a letter or _ that is not True or False.

Environment (please complete the following information):

• OS: iOS
• JDK/JRE version = 17.0.8.1-tem
• RgxGen Version = 2.0

[curious-odd-man]

Thank you for reporting this.

Adding some examples for myself: