Add SA1019 suppression for intentionally retained deprecated spec.Subnet field

[coderabbitai]

Summary

The --subnet CLI flag in internal/cmd/cli/create/computeinstance/create_compute_instance_cmd.go intentionally writes to the deprecated protobuf field spec.Subnet for backward compatibility. This causes staticcheck to emit SA1019 at line 769, which can block lint gates.

Severity: Medium — lint gate breakage risk if SA1019 is enforced in CI.
Impact: CI pipelines running staticcheck or golangci-lint with SA1019 enabled will fail until a targeted suppression is added.

Background

• The --subnet flag is deprecated in favour of --network-attachment, but is intentionally retained for backward compatibility.
• PR NO-ISSUE: Use new(expression) syntax from Go 1.26 fulfillment-service#610 (mechanical go fix -newexpr refactor) changed proto.String(c.args.subnet) → new(c.args.subnet) at line 769; the SA1019 concern is a pre-existing issue separate from that refactor and was deferred out of scope.
• Related comment: NO-ISSUE: Use new(expression) syntax from Go 1.26 fulfillment-service#610 (comment)

Proposed fix

Add a targeted lint suppression directly above the assignment with a rationale comment, for example:

if c.args.subnet != "" {
    //nolint:staticcheck // Intentionally retained for backward compatibility with deprecated --subnet flag.
    spec.Subnet = new(c.args.subnet)
}

References

• PR: NO-ISSUE: Use new(expression) syntax from Go 1.26 fulfillment-service#610
• Requested by: @jhernand