Use std::tmpfile in create_file on Windows

[bugdea1er]

Instead of dealing with signals, file permissions and such, delegate it to std::tmpfile

After creating the file, we can simply std::freopen the file with the desired openmode

Part of #193 for Windows

[Copilot]

Pull Request Overview

A Windows-specific refactor to use std::tmpfile for temporary file creation and then reopen it with the requested mode, removing manual signal/permission handling.

• Introduce a create_file(mode, ec) overload that delegates to std::tmpfile and uses Windows APIs to recover the file path and reopen it.
• Simplify the existing create_file(mode) on Windows to call the new overload and convert errors to std::filesystem_error.
• Update tests to drop the hardlink count assertion under the Windows branch.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
tests/file.cpp	Removed the hardlink-count check from the Windows test path.
src/create.cpp	Added _CRT_SECURE_NO_WARNINGS, included platform headers, and implemented the std::tmpfile–based create_file.

Comments suppressed due to low confidence (1)

tests/file.cpp:77

• [nitpick] The hardlink-count assertion was removed from the Windows test path, potentially reducing coverage of link-related behavior. If ensuring no hardlinks is still important, consider adding a Windows-specific check or replacing this assertion with an equivalent check.

EXPECT_EQ(file_info.nNumberOfLinks, 0);    // Has no hardlinks