perf(quickemu): enable TRIM/discard and detect-zeroes for qcow2 drives

[flexiondotorg]

Enabling discard=unmap passes guest TRIM requests through to the qcow2
layer, allowing automatic disk space reclamation as guests delete files,
while detect-zeroes=unmap converts zero-block writes into additional
discard operations for further space savings. This configuration mirrors
Proxmox VE's default settings, where it has proven stable across millions
of production VMs since QEMU 1.5.

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• I have performed a self-review of my code

[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.