Validate native CoW reflinks on XFS (with reflink=1)

[Rakshat28]

XFS is the standard filesystem for many enterprise Linux distros (like RHEL/Fedora) and supports CoW reflinks, but only if formatted with the reflink=1 flag. We need to ensure bdstorage correctly utilizes XFS block cloning and handles sparse files correctly on this filesystem.

Acceptance Criteria:

• Add a step in .github/workflows/ci.yml to create and mount an xfs loopback device using mkfs.xfs -m reflink=1.
• Run the integration test suite against the XFS mount.
• Verify that the sparse-hashing math behaves correctly with XFS's specific extent allocation strategies.