Clean up warning and build artifact

With pytest with python 3.14 I get the following warning: 
```
fparser/two/pattern_tools.py:70: SyntaxWarning: "\:" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\\:"? A raw string is also an option.
```

Also the when using fparser as a submodule the pip "build" artifact is generated, it would be good to gitignore it.