fix: normalize Windows backslash paths to forward slashes in image upload

[Copilot]

Summary

Fixes #361

On Windows, when uploading an image via source_image_path or cd_files, the full Windows path (in 8.3 notation, e.g. C:\USERS\J81BLO~1\image.iso) was appearing as the image name in Prism Central instead of just the filename.

Root cause

There were two related issues in driver.go:

1. CreateImageURL — path.Split(disk.SourceImageURI) only recognises / as a path separator. Any URI that contains Windows-style backslashes (e.g. file:///C:\path\image.iso) would have the full path returned as the "filename".

2. CreateImageFile — filepath.Split(filePath) is OS-specific and correctly handles \ on a Windows binary. However, the raw filePath (with backslashes) was then forwarded to the SDK's Images.Upload. The SDK derives the image name internally via filepath.Base(sourcePath). On Linux builds (cross-compiled binaries, WSL, MSYS2, Git Bash), filepath.Base does not recognise \ as a separator and returns the entire path as the filename — causing the full Windows path to become the image name in Prism Central.

Fix

Normalize all backslash separators to forward slashes before any path extraction or SDK call:

• CreateImageURL: replace path.Split(disk.SourceImageURI) with path.Base(strings.ReplaceAll(…, "\\", "/")).
• CreateImageFile: compute normalizedPath with strings.ReplaceAll(filePath, "\\", "/"), extract file using path.Base(normalizedPath), and pass normalizedPath to v4Client.Images.Upload so the SDK's internal filepath.Base call also produces the correct basename. Windows accepts / as a path separator in all standard file-open calls, so os.Open continues to work correctly.
• Remove the now-unused path/filepath import.

Testing

• go build ./... and go test ./... pass cleanly.
• The fix is backward-compatible: Linux paths never contain \, so strings.ReplaceAll is a no-op for them.