fix(stdlib-stubs): promote os.statvfs and os.sync out of platform conditionals

[Copilot]

Typeshed gates os.statvfs and os.sync inside if sys.platform != "win32": blocks. After docstub enrichment those functions gained MicroPython docs/types but stayed inside the conditional — so on Windows, pyright evaluates the guard as False and hides them, making from os import statvfs report an unknown import symbol.

Changes

build.py — new post-merge step

• Adds promote_mp_available_from_conditionals(folder), called after merge_docstubs_into_stdlib().
• Scans os/__init__.pyi for top-level if sys.platform blocks where every def is immediately preceded by @mp_available().
• For matching blocks: comments out the conditional header and de-indents the body to module level.
• Blocks with any undecorated def (e.g. mkfifo) are left untouched.

stdlib/os/__init__.pyi — checked-in output updated

• statvfs and sync are now unconditionally available at module level; their if sys.platform != "win32": headers are commented out.

# if sys.platform != "win32":

@mp_available()  # force merge
def statvfs(path) -> Tuple: ...

@mp_available()  # force merge
def sync() -> None: ...

Closes: #903

[Josverl]

Just check for @mpavailable, it may not have () , it may have parameters

[Copilot]

Fixed in the latest commit — both has_mp_available and the has_undecorated_def check now use startswith("@mp_available") instead of the exact "@mp_available()" string, so bare @mp_available, @mp_available(), and @mp_available(some_arg) all match correctly.

[Josverl]

another possible match is : folder / module / f"{module}.pyi"

solve by checking alist of options , rather than nested if statements

[Copilot]

Fixed in the latest commit — replaced the nested if with a candidates list (__init__.pyi, {module}/{module}.pyi, {module}.pyi) and a single next(... if p.exists(), None) lookup.