Run tests on all platforms

[peterjan]

Closes #130

[Copilot]

Pull request overview

This PR updates CI and some filesystem handling to enable running the Go test suite across platforms (Windows/macOS/Linux), addressing platform-specific file deletion semantics and test resource cleanup.

Changes:

• Switch CI to a shared reusable Go test workflow (intended to run on multiple OSes) and enable CGO for sqlite.
• Add OS-specific openFileAllowDelete to allow reading files while they may be deleted on Windows; update upload reads to use it.
• Improve sqlite test/benchmark cleanup by closing the database store; remove multipart parent-directory sync calls.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
sia/persist/sqlite/objects_test.go	Adds Cleanup hooks to close sqlite store after tests/benchmarks.
sia/open_file_windows.go	Windows-specific file open allowing delete sharing via CreateFile.
sia/open_file_nonwindows.go	Non-Windows implementation using os.Open.
sia/objects.go	Uses openFileAllowDelete when reading an upload file.
sia/multipart.go	Removes parent-directory sync step after writing multipart parts.
.github/workflows/go-test.yml	Replaces in-repo steps with a reusable workflow call; adds push trigger and sets CGO_ENABLED.

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