Windows-style paths

[ruairi]

Describe the bug

Backslash messes up things when local open is used:

[INFO] Building optimizer
error: failed to parse manifest at `D:\PycharmProjects\OpEn_Fix_107\open-codegen\opengen\my_optimizers\rosenbrock\Cargo.toml`
Caused by:
  could not parse input as TOML
Caused by:
  TOML parse error at line 19, column 35
     |
  19 | optimization_engine = {path = "D:\PycharmProjects\OpEn_Fix_107\"}
     |                                   ^
  Unexpected `P`
  While parsing escape sequence
  While parsing a Basic String
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "C:\Program Files\JetBrains\PyCharm 2021.2.3\plugins\python\helpers\pydev\_pydev_bundle\pydev_umd.py", line 198, in runfile
    pydev_imports.execfile(filename, global_vars, local_vars)  # execute the script
  File "C:\Program Files\JetBrains\PyCharm 2021.2.3\plugins\python\helpers\pydev\_pydev_imps\_pydev_execfile.py", line 18, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "D:/PycharmProjects/OpEn_Fix_107/open-codegen/opengen/main.py", line 47, in <module>
    builder.build()
  File "D:\PycharmProjects\OpEn_Fix_107\venv\lib\site-packages\opengen\builder\optimizer_builder.py", line 804, in build
    self.__build_optimizer()             # build overall project
  File "D:\PycharmProjects\OpEn_Fix_107\venv\lib\site-packages\opengen\builder\optimizer_builder.py", line 570, in __build_optimizer
    raise Exception('Rust build failed')
Exception: Rust build failed

The issue has been analysed to be due to the function get_open_local_absolute_path() in main.py providing an address path incompatible with windows.

To Reproduce

Use with_open_version(local_path=...) on Windows. We need get_open_local_absolute_path() to return paths with forward slashes both on Windows and Linux/MacOS.

System information:

• Windows