Simplify character and string literal parsing logic

[mizdebsk]

Refactor and simplify parsing logic for character and string literals within find_token(). Merge redundant conditional branches, reduce unnecessary control flow, and replace multi-line loops with more concise equivalents.

[mizdebsk]

This is an alternative to #28 that not only fixes static analysis warnings, but also simplifies code logic.

[mkoncek]

When looking at this, I realize why I wrote it like I did. I find the verbose code actually more readable. It almost reads like a sentence. I don't like compressing more operations into a single line.
An optimizing compiler has no problems deduplicating things like substr.
So I am not in favor of this change.

[mizdebsk]

Feel free to close it in favor of #28, which preserves readability.